Address 2 crashes in download attribution code

chrome/browser/safe_browsing/safe_browsing_navigation_observer_browsertest.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/strings/stringprintf.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/download/download_prefs.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/safe_browsing/download_protection_service.h"
 #include "chrome/browser/safe_browsing/safe_browsing_navigation_observer.h"
@@ skipping 15 matching lines @@
 #include "content/public/test/test_utils.h"
 #include "net/dns/mock_host_resolver.h"
 #include "net/test/embedded_test_server/embedded_test_server.h"
 #include "url/gurl.h"
 #include "url/url_canon.h"
 
 using content::DownloadItem;
 
 namespace safe_browsing {
 
+typedef SafeBrowsingNavigationObserverManager::ReferrerChain ReferrerChain;
+
 const char kSingleFrameTestURL[] =
     "/safe_browsing/download_protection/navigation_observer/"
     "navigation_observer_tests.html";
 const char kMultiFrameTestURL[] =
     "/safe_browsing/download_protection/navigation_observer/"
     "navigation_observer_multi_frame_tests.html";
 const char kRedirectURL[] =
     "/safe_browsing/download_protection/navigation_observer/redirect.html";
 const char kDownloadDataURL[] =
     "data:application/octet-stream;base64,a2poYWxrc2hkbGtoYXNka2xoYXNsa2RoYWxra"
@@ skipping 181 matching lines @@
     EXPECT_EQ(expected_has_server_redirect,
               actual_nav_event.has_server_redirect);
   }
 
   void VerifyReferrerChainEntry(const GURL& expected_url,
                                 ReferrerChainEntry::URLType expected_type,
                                 const std::string& expected_ip_address,
                                 const GURL& expected_referrer_url,
                                 const GURL& expected_referrer_main_frame_url,
                                 bool expected_is_retargeting,
-                                ReferrerChainEntry actual_entry) {
-    EXPECT_EQ(expected_url.spec(), actual_entry.url());
-    EXPECT_EQ(expected_type, actual_entry.type());
+                                ReferrerChainEntry* actual_entry) {
+    EXPECT_EQ(expected_url.spec(), actual_entry->url());
+    EXPECT_EQ(expected_type, actual_entry->type());
     if (expected_ip_address.empty()) {
-      ASSERT_EQ(0, actual_entry.ip_addresses_size());
+      ASSERT_EQ(0, actual_entry->ip_addresses_size());
     } else {
-      ASSERT_EQ(1, actual_entry.ip_addresses_size());
-      EXPECT_EQ(expected_ip_address, actual_entry.ip_addresses(0));
+      ASSERT_EQ(1, actual_entry->ip_addresses_size());
+      EXPECT_EQ(expected_ip_address, actual_entry->ip_addresses(0));
     }
-    EXPECT_EQ(expected_referrer_url.spec(), actual_entry.referrer_url());
+    EXPECT_EQ(expected_referrer_url.spec(), actual_entry->referrer_url());
     EXPECT_EQ(expected_referrer_main_frame_url.spec(),
-              actual_entry.referrer_main_frame_url());
-    EXPECT_EQ(expected_is_retargeting, actual_entry.is_retargeting());
+              actual_entry->referrer_main_frame_url());
+    EXPECT_EQ(expected_is_retargeting, actual_entry->is_retargeting());
   }
 
-  std::vector<ReferrerChainEntry> IdentifyReferrerChainForDownload(
-      DownloadItem* download) {
-    std::vector<ReferrerChainEntry> referrer_chain;
+  // Identify referrer chain of a DownloadItem and populate |referrer_chain|.
+  void IdentifyReferrerChainForDownload(
+      DownloadItem* download,
+      ReferrerChain* referrer_chain) {
     int download_tab_id =
         SessionTabHelper::IdForTab(download->GetWebContents());
     // IdentifyReferrerChain should return SUCCESS(1), SUCCESS_LANDING_PAGE(2),
     // or SUCCESS_LANDING_REFERRER(3) in all these tests.
     EXPECT_LE(observer_manager_->IdentifyReferrerChainForDownload(
                   download->GetURL(), download_tab_id,
                   2,  // kDownloadAttributionUserGestureLimit
-                  &referrer_chain),
+                  referrer_chain),
               SafeBrowsingNavigationObserverManager::SUCCESS_LANDING_REFERRER);
-    return referrer_chain;
   }
 
-  std::vector<ReferrerChainEntry> IdentifyReferrerChainForPPAPIDownload(
+  // Identify referrer chain of a PPAPI download and populate |referrer_chain|.
+  void IdentifyReferrerChainForPPAPIDownload(
       const GURL& initiating_frame_url,
-      content::WebContents* web_contents) {
-    std::vector<ReferrerChainEntry> referrer_chain;
+      content::WebContents* web_contents,
+      ReferrerChain* referrer_chain) {
     int tab_id = SessionTabHelper::IdForTab(web_contents);
     bool has_user_gesture = observer_manager_->HasUserGesture(web_contents);
     observer_manager_->OnUserGestureConsumed(web_contents, base::Time::Now());
     EXPECT_LE(observer_manager_->IdentifyReferrerChainForPPAPIDownload(
                   initiating_frame_url,
                   tab_id,
                   has_user_gesture,
                   2,  // kDownloadAttributionUserGestureLimit)
-                  &referrer_chain),
+                  referrer_chain),
               SafeBrowsingNavigationObserverManager::SUCCESS_LANDING_REFERRER);
-    return referrer_chain;
   }
 
   void VerifyHostToIpMap() {
     // Since all testing pages have the same host, there is only one entry in
     // host_to_ip_map_.
     SafeBrowsingNavigationObserverManager::HostToIpMap* actual_host_ip_map =
         host_to_ip_map();
     ASSERT_EQ(1U, actual_host_ip_map->size());
     auto ip_list =
         actual_host_ip_map->at(embedded_test_server()->base_url().host());
@@ skipping 47 matching lines @@
   VerifyNavigationEvent(GURL(),        // source_url
                         GURL(),        // source_main_frame_url
                         download_url,  // original_request_url
                         download_url,  // destination_url
                         true,          // is_user_initiated,
                         false,         // has_committed
                         false,         // has_server_redirect
                         nav_map->at(download_url).at(0));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
   ASSERT_EQ(1U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,   // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
 }
 // Click on a link and start download on the same page.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest, DirectDownload) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("direct_download", 1, initial_url);
   GURL download_url = embedded_test_server()->GetURL(kDownloadItemURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
   auto nav_map = navigation_map();
   ASSERT_TRUE(nav_map);
   ASSERT_EQ(2U, nav_map->size());
@@ skipping 10 matching lines @@
   VerifyNavigationEvent(initial_url,   // source_url
                         initial_url,   // source_main_frame_url
                         download_url,  // original_request_url
                         download_url,  // destination_url
                         true,          // is_user_initiated,
                         false,         // has_committed
                         false,         // has_server_redirect
                         nav_map->at(download_url).at(0));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
   ASSERT_EQ(2U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            initial_url,                       // referrer_url
                            initial_url,  // referrer_main_frame_url
                            false,        // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(initial_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,   // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
 }
 
 // Click on a link with rel="noreferrer" attribute, and start download on the
 // same page.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
                        DirectDownloadNoReferrer) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("direct_download_noreferrer", 1, initial_url);
   GURL download_url = embedded_test_server()->GetURL(kDownloadItemURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
@@ skipping 13 matching lines @@
   VerifyNavigationEvent(initial_url,   // source_url
                         initial_url,   // source_main_frame_url
                         download_url,  // original_request_url
                         download_url,  // destination_url
                         true,          // is_user_initiated,
                         false,         // has_committed
                         false,         // has_server_redirect
                         nav_map->at(download_url).at(0));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
   ASSERT_EQ(2U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            initial_url,                       // referrer_url
                            initial_url,  // referrer_main_frame_url
                            false,        // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(initial_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,   // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
 }
 
 // Click on a link with rel="noreferrer" attribute, and start download in a
 // new tab using target=_blank.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
                        DirectDownloadNoReferrerTargetBlank) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("direct_download_noreferrer_target_blank", 1, initial_url);
   GURL download_url = embedded_test_server()->GetURL(kDownloadItemURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
@@ skipping 27 matching lines @@
   VerifyNavigationEvent(GURL(),        // source_url
                         GURL(),        // source_main_frame_url
                         download_url,  // original_request_url
                         download_url,  // destination_url
                         false,         // is_user_initiated,
                         false,         // has_committed
                         false,         // has_server_redirect
                         nav_map->at(download_url).at(1));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
   ASSERT_EQ(2U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            initial_url,                       // referrer_url
                            initial_url,  // referrer_main_frame_url
                            true,         // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(initial_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,   // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
 }
 
 // Click on a link which navigates to a page then redirects to a download using
 // META HTTP-EQUIV="refresh". All transitions happen in the same tab.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
                        SingleMetaRefreshRedirect) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("single_meta_refresh_redirect", 2, initial_url);
   GURL redirect_url = embedded_test_server()->GetURL(kRedirectURL);
   GURL download_url = embedded_test_server()->GetURL(kDownloadItemURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
   auto nav_map = navigation_map();
   ASSERT_TRUE(nav_map);
   // Since unlike server redirects client redirects commit and then generate a
   // second navigation, our observer records two NavigationEvents for this test.
-  ASSERT_EQ(std::size_t(3), nav_map->size());
+  ASSERT_EQ(3U, nav_map->size());
   ASSERT_EQ(1U, nav_map->at(redirect_url).size());
   ASSERT_EQ(1U, nav_map->at(download_url).size());
   ASSERT_EQ(1U, nav_map->at(initial_url).size());
   VerifyNavigationEvent(GURL(),       // source_url
                         GURL(),       // source_main_frame_url
                         initial_url,  // original_request_url
                         initial_url,  // destination_url
                         true,         // is_user_initiated,
                         true,         // has_committed
                         false,        // has_server_redirect
                         nav_map->at(initial_url).at(0));
   VerifyNavigationEvent(initial_url,   // source_url
                         initial_url,   // source_main_frame_url
                         redirect_url,  // original_request_url
                         redirect_url,  // destination_url
                         true,          // is_user_initiated,
                         true,          // has_committed
                         false,         // has_server_redirect
                         nav_map->at(redirect_url).at(0));
   VerifyNavigationEvent(redirect_url,  // source_url
                         redirect_url,  // source_main_frame_url
                         download_url,  // original_request_url
                         download_url,  // destination_url
                         false,         // is_user_initiated,
                         false,         // has_committed
                         false,         // has_server_redirect
                         nav_map->at(download_url).at(0));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
-  ASSERT_EQ(std::size_t(3), referrer_chain.size());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
+  ASSERT_EQ(3U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            redirect_url,                      // referrer_url
                            redirect_url,  // referrer_main_frame_url
                            false,         // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(redirect_url,                         // url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            test_server_ip,                       // ip_address
                            initial_url,                          // referrer_url
                            initial_url,  // referrer_main_frame_url
                            false,        // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
   VerifyReferrerChainEntry(initial_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,   // is_retargeting
-                           referrer_chain[2]);
+                           referrer_chain[2].get());
 }
 
 // Click on a link which navigates to a page then redirects to a download using
 // META HTTP-EQUIV="refresh". First navigation happens in target blank.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
                        SingleMetaRefreshRedirectTargetBlank) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("single_meta_refresh_redirect_target_blank", 2, initial_url);
   GURL redirect_url = embedded_test_server()->GetURL(kRedirectURL);
   GURL download_url = embedded_test_server()->GetURL(kDownloadItemURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
   auto nav_map = navigation_map();
   ASSERT_TRUE(nav_map);
-  ASSERT_EQ(std::size_t(3), nav_map->size());
+  ASSERT_EQ(3U, nav_map->size());
   ASSERT_EQ(2U, nav_map->at(redirect_url).size());
   ASSERT_EQ(1U, nav_map->at(download_url).size());
   ASSERT_EQ(1U, nav_map->at(initial_url).size());
   VerifyNavigationEvent(GURL(),       // source_url
                         GURL(),       // source_main_frame_url
                         initial_url,  // original_request_url
                         initial_url,  // destination_url
                         true,         // is_user_initiated,
                         true,         // has_committed
                         false,        // has_server_redirect
@@ skipping 20 matching lines @@
   VerifyNavigationEvent(redirect_url,  // source_url
                         redirect_url,  // source_main_frame_url
                         download_url,  // original_request_url
                         download_url,  // destination_url
                         false,         // is_user_initiated,
                         false,         // has_committed
                         false,         // has_server_redirect
                         nav_map->at(download_url).at(0));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
-  ASSERT_EQ(std::size_t(3), referrer_chain.size());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
+  ASSERT_EQ(3U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            redirect_url,                      // referrer_url
                            redirect_url,  // referrer_main_frame_url
                            false,         // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(redirect_url,                         // url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            test_server_ip,                       // ip_address
                            initial_url,                          // referrer_url
                            initial_url,  // referrer_main_frame_url
                            true,         // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
   VerifyReferrerChainEntry(initial_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,   // is_retargeting
-                           referrer_chain[2]);
+                           referrer_chain[2].get());
 }
 
 // Click on a link which redirects twice before reaching download using
 // META HTTP-EQUIV="refresh". All transitions happen in the same tab.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
                        MultiMetaRefreshRedirects) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("multiple_meta_refresh_redirects", 3, initial_url);
   GURL first_redirect_url = embedded_test_server()->GetURL(
       "/safe_browsing/download_protection/navigation_observer/"
       "double_redirect.html");
   GURL second_redirect_url = embedded_test_server()->GetURL(kRedirectURL);
   GURL download_url = embedded_test_server()->GetURL(kDownloadItemURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
   auto nav_map = navigation_map();
   ASSERT_TRUE(nav_map);
-  ASSERT_EQ(std::size_t(4), nav_map->size());
+  ASSERT_EQ(4U, nav_map->size());
   ASSERT_EQ(1U, nav_map->at(first_redirect_url).size());
   ASSERT_EQ(1U, nav_map->at(second_redirect_url).size());
   ASSERT_EQ(1U, nav_map->at(download_url).size());
   ASSERT_EQ(1U, nav_map->at(initial_url).size());
   VerifyNavigationEvent(GURL(),       // source_url
                         GURL(),       // source_main_frame_url
                         initial_url,  // original_request_url
                         initial_url,  // destination_url
                         true,         // is_user_initiated,
                         true,         // has_committed
@@ skipping 18 matching lines @@
   VerifyNavigationEvent(second_redirect_url,  // source_url
                         second_redirect_url,  // source_main_frame_url
                         download_url,         // original_request_url
                         download_url,         // destination_url
                         false,                // is_user_initiated,
                         false,                // has_committed
                         false,                // has_server_redirect
                         nav_map->at(download_url).at(0));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
-  ASSERT_EQ(std::size_t(4), referrer_chain.size());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
+  ASSERT_EQ(4U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            second_redirect_url,               // referrer_url
                            second_redirect_url,  // referrer_main_frame_url
                            false,                // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(second_redirect_url,                  // url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            test_server_ip,                       // ip_address
                            first_redirect_url,                   // referrer_url
                            first_redirect_url,  // referrer_main_frame_url
                            false,               // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
   VerifyReferrerChainEntry(first_redirect_url,                   // url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            test_server_ip,                       // ip_address
                            initial_url,                          // referrer_url
                            initial_url,  // referrer_main_frame_url
                            false,        // is_retargeting
-                           referrer_chain[2]);
+                           referrer_chain[2].get());
   VerifyReferrerChainEntry(initial_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,   // is_retargeting
-                           referrer_chain[3]);
+                           referrer_chain[3].get());
 }
 
 // Click on a link which redirects to download using window.location.
 // All transitions happen in the same tab.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
                        WindowLocationRedirect) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("window_location_redirection", 1, initial_url);
   GURL download_url = embedded_test_server()->GetURL(kDownloadItemURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
@@ skipping 12 matching lines @@
                         nav_map->at(initial_url).at(0));
   VerifyNavigationEvent(initial_url,   // source_url
                         initial_url,   // source_main_frame_url
                         download_url,  // original_request_url
                         download_url,  // destination_url
                         true,          // is_user_initiated,
                         false,         // has_committed
                         false,         // has_server_redirect
                         nav_map->at(download_url).at(0));
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
   ASSERT_EQ(2U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            initial_url,                       // referrer_url
                            initial_url,  // referrer_main_frame_url
                            false,        // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(initial_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,   // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
 }
 
 // Click on a link which redirects twice until it reaches download using a
 // mixture of meta refresh and window.location. All transitions happen in the
 // same tab.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest, MixRedirects) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("mix_redirects", 2, initial_url);
   GURL redirect_url = embedded_test_server()->GetURL(kRedirectURL);
   GURL download_url = embedded_test_server()->GetURL(kDownloadItemURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
   auto nav_map = navigation_map();
   ASSERT_TRUE(nav_map);
-  ASSERT_EQ(std::size_t(3), nav_map->size());
+  ASSERT_EQ(3U, nav_map->size());
   ASSERT_EQ(1U, nav_map->at(redirect_url).size());
   ASSERT_EQ(1U, nav_map->at(download_url).size());
   ASSERT_EQ(1U, nav_map->at(initial_url).size());
   VerifyNavigationEvent(GURL(),       // source_url
                         GURL(),       // source_main_frame_url
                         initial_url,  // original_request_url
                         initial_url,  // destination_url
                         true,         // is_user_initiated,
                         true,         // has_committed
                         false,        // has_server_redirect
                         nav_map->at(initial_url).at(0));
   VerifyNavigationEvent(initial_url,   // source_url
                         initial_url,   // source_main_frame_url
                         redirect_url,  // original_request_url
                         redirect_url,  // destination_url
                         true,          // is_user_initiated,
                         true,          // has_committed
                         false,         // has_server_redirect
                         nav_map->at(redirect_url).at(0));
   VerifyNavigationEvent(redirect_url,  // source_url
                         redirect_url,  // source_main_frame_url
                         download_url,  // original_request_url
                         download_url,  // destination_url
                         false,         // is_user_initiated,
                         false,         // has_committed
                         false,         // has_server_redirect
                         nav_map->at(download_url).at(0));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
-  ASSERT_EQ(std::size_t(3), referrer_chain.size());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
+  ASSERT_EQ(3U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            redirect_url,                      // referrer_url
                            redirect_url,  // referrer_main_frame_url
                            false,         // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(redirect_url,                         // url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            test_server_ip,                       // ip_address
                            initial_url,                          // referrer_url
                            initial_url,  // referrer_main_frame_url
                            false,        // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
   VerifyReferrerChainEntry(initial_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,   // is_retargeting
-                           referrer_chain[2]);
+                           referrer_chain[2].get());
 }
 
 // Use javascript to open download in a new tab.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest, NewTabDownload) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("new_tab_download", 2, initial_url);
   GURL download_url = embedded_test_server()->GetURL(kDownloadItemURL);
   GURL blank_url = GURL(url::kAboutBlankURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
   auto nav_map = navigation_map();
   ASSERT_TRUE(nav_map);
-  ASSERT_EQ(std::size_t(3), nav_map->size());
+  ASSERT_EQ(3U, nav_map->size());
   ASSERT_EQ(2U, nav_map->at(blank_url).size());
   ASSERT_EQ(1U, nav_map->at(download_url).size());
   ASSERT_EQ(1U, nav_map->at(initial_url).size());
   VerifyNavigationEvent(GURL(),       // source_url
                         GURL(),       // source_main_frame_url
                         initial_url,  // original_request_url
                         initial_url,  // destination_url
                         true,         // is_user_initiated,
                         true,         // has_committed
                         false,        // has_server_redirect
@@ skipping 24 matching lines @@
                         download_url,  // original_request_url
                         download_url,  // destination_url
                         false,         // is_user_initiated,
                         false,         // has_committed
                         false,         // has_server_redirect
                         nav_map->at(download_url).at(0));
   EXPECT_EQ(nav_map->at(download_url).at(0).source_tab_id,
             nav_map->at(download_url).at(0).target_tab_id);
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
-  ASSERT_EQ(std::size_t(3), referrer_chain.size());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
+  ASSERT_EQ(3U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            blank_url,                         // referrer_url
                            blank_url,  // referrer_main_frame_url
                            false,      // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(blank_url,                            // url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            "",                                   // ip_address
                            initial_url,                          // referrer_url
                            initial_url,  // referrer_main_frame_url
                            true,         // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
   VerifyReferrerChainEntry(initial_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,   // is_retargeting
-                           referrer_chain[2]);
+                           referrer_chain[2].get());
 }
 
 // Use javascript to open download in a new tab and download has a data url.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
                        NewTabDownloadWithDataURL) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("new_tab_download_with_data_url", 2, initial_url);
   GURL download_url = GURL(kDownloadDataURL);
   GURL blank_url = GURL(url::kAboutBlankURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
   auto nav_map = navigation_map();
   ASSERT_TRUE(nav_map);
-  ASSERT_EQ(std::size_t(3), nav_map->size());
+  ASSERT_EQ(3U, nav_map->size());
   ASSERT_EQ(2U, nav_map->at(blank_url).size());
   ASSERT_EQ(1U, nav_map->at(download_url).size());
   ASSERT_EQ(1U, nav_map->at(initial_url).size());
   VerifyNavigationEvent(GURL(),       // source_url
                         GURL(),       // source_main_frame_url
                         initial_url,  // original_request_url
                         initial_url,  // destination_url
                         true,         // is_user_initiated,
                         true,         // has_committed
                         false,        // has_server_redirect
@@ skipping 25 matching lines @@
                         download_url,  // original_request_url
                         download_url,  // destination_url
                         false,         // is_user_initiated,
                         false,         // has_committed
                         false,         // has_server_redirect
                         nav_map->at(download_url).at(0));
   EXPECT_TRUE(nav_map->at(download_url).at(0).source_tab_id ==
               nav_map->at(download_url).at(0).target_tab_id);
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
-  ASSERT_EQ(std::size_t(3), referrer_chain.size());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
+  ASSERT_EQ(3U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            "",                                // ip_address
                            blank_url,                         // referrer_url
                            blank_url,  // referrer_main_frame_url
                            false,      // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(blank_url,                            // url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            "",                                   // ip_address
                            initial_url,                          // referrer_url
                            initial_url,  // referrer_main_frame_url
                            true,         // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
   VerifyReferrerChainEntry(initial_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,   // is_retargeting
-                           referrer_chain[2]);
+                           referrer_chain[2].get());
 }
 
 // TODO(jialiul): Need to figure out why this test is failing on Windows and
 // flaky on other platforms.
 #define MAYBE_DownloadViaHTML5FileApi DISABLED_DownloadViaHTML5FileApi
 // Download via html5 file API.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
                        MAYBE_DownloadViaHTML5FileApi) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("html5_file_api", 1, initial_url);
@@ skipping 18 matching lines @@
   VerifyNavigationEvent(initial_url,   // source_url
                         initial_url,   // source_main_frame_url
                         download_url,  // original_request_url
                         download_url,  // destination_url
                         true,          // is_user_initiated,
                         false,         // has_committed
                         false,         // has_server_redirect
                         nav_map->at(download_url).at(0));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
   ASSERT_EQ(2U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            "",                                // ip_address
                            initial_url,                       // referrer_url
                            initial_url,  // referrer_main_frame_url
                            false,        // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(initial_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,   // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
 }
 
 // Click a link in a subframe and start download.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
                        SubFrameDirectDownload) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("sub_frame_download_attribution", 1, initial_url);
   std::string test_name =
       base::StringPrintf("%s', '%s", "iframe1", "iframe_direct_download");
   GURL multi_frame_test_url =
       embedded_test_server()->GetURL(kMultiFrameTestURL);
   GURL iframe_url = embedded_test_server()->GetURL(kIframeDirectDownloadURL);
   ClickTestLink(test_name.c_str(), 1, iframe_url);
   GURL iframe_retargeting_url =
       embedded_test_server()->GetURL(kIframeRetargetingURL);
   GURL download_url = embedded_test_server()->GetURL(kDownloadItemURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
   auto nav_map = navigation_map();
   ASSERT_TRUE(nav_map);
-  ASSERT_EQ(std::size_t(5), nav_map->size());
+  ASSERT_EQ(5U, nav_map->size());
   ASSERT_EQ(1U, nav_map->at(multi_frame_test_url).size());
   ASSERT_EQ(1U, nav_map->at(iframe_url).size());
   ASSERT_EQ(1U, nav_map->at(iframe_retargeting_url).size());
   ASSERT_EQ(1U, nav_map->at(download_url).size());
   ASSERT_EQ(1U, nav_map->at(initial_url).size());
   VerifyNavigationEvent(GURL(),       // source_url
                         GURL(),       // source_main_frame_url
                         initial_url,  // original_request_url
                         initial_url,  // destination_url
                         true,         // is_user_initiated,
@@ skipping 27 matching lines @@
   VerifyNavigationEvent(iframe_url,            // source_url
                         multi_frame_test_url,  // source_main_frame_url
                         download_url,          // original_request_url
                         download_url,          // destination_url
                         true,                  // is_user_initiated,
                         false,                 // has_committed
                         false,                 // has_server_redirect
                         nav_map->at(download_url).at(0));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
   ASSERT_EQ(4U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            iframe_url,                        // referrer_url
                            multi_frame_test_url,  // referrer_main_frame_url
                            false,                 // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(iframe_url,                        // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            multi_frame_test_url,  // referrer_main_frame_url
                            false,                 // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
   VerifyReferrerChainEntry(multi_frame_test_url,                 // url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            test_server_ip,                       // ip_address
                            initial_url,  // referrer_url
                            initial_url,  // referrer_main_frame_url
                            false,                 // is_retargeting
-                           referrer_chain[2]);
+                           referrer_chain[2].get());
   VerifyReferrerChainEntry(initial_url,                           // url
                            ReferrerChainEntry::LANDING_REFERRER,  // type
                            test_server_ip,                        // ip_address
                            GURL(),  // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,                 // is_retargeting
-                           referrer_chain[3]);
+                           referrer_chain[3].get());
 }
 
 // Click a link in a subframe and open download in a new tab.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
                        SubFrameNewTabDownload) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("sub_frame_download_attribution", 1, initial_url);
   std::string test_name =
       base::StringPrintf("%s', '%s", "iframe2", "iframe_new_tab_download");
   GURL multi_frame_test_url =
@@ skipping 65 matching lines @@
   VerifyNavigationEvent(blank_url,     // source_url
                         blank_url,     // source_main_frame_url
                         download_url,  // original_request_url
                         download_url,  // destination_url
                         false,         // is_user_initiated,
                         false,         // has_committed
                         false,         // has_server_redirect
                         nav_map->at(download_url).at(0));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
   EXPECT_EQ(5U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            blank_url,                         // referrer_url
                            blank_url,  // referrer_main_frame_url
                            false,      // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(blank_url,                            // url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            "",                                   // ip_address
                            iframe_retargeting_url,               // referrer_url
                            multi_frame_test_url,  // referrer_main_frame_url
                            true,                  // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
   VerifyReferrerChainEntry(iframe_retargeting_url,            // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            multi_frame_test_url,  // referrer_main_frame_url
                            false,                 // is_retargeting
-                           referrer_chain[2]);
+                           referrer_chain[2].get());
   VerifyReferrerChainEntry(multi_frame_test_url,                 // url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            test_server_ip,                       // ip_address
                            initial_url,  // referrer_url
                            initial_url,  // referrer_main_frame_url
                            false,                 // is_retargeting
-                           referrer_chain[3]);
+                           referrer_chain[3].get());
   VerifyReferrerChainEntry(initial_url,                           // url
                            ReferrerChainEntry::LANDING_REFERRER,  // type
                            test_server_ip,                        // ip_address
                            GURL(),  // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,                 // is_retargeting
-                           referrer_chain[4]);
+                           referrer_chain[4].get());
 }
 
 // Click a link which redirects to the landing page, and then click on the
 // landing page to trigger download.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest, CompleteReferrerChain) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("complete_referrer_chain", 2, initial_url);
   GURL redirect_url = embedded_test_server()->GetURL(kRedirectToLandingURL);
   GURL landing_url = embedded_test_server()->GetURL(kLandingURL);
   ClickTestLink("download_on_landing_page", 1, landing_url);
   GURL download_url = embedded_test_server()->GetURL(kDownloadItemURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
   auto nav_map = navigation_map();
   ASSERT_TRUE(nav_map);
-  ASSERT_EQ(std::size_t(4), nav_map->size());
+  ASSERT_EQ(4U, nav_map->size());
   ASSERT_EQ(1U, nav_map->at(redirect_url).size());
   ASSERT_EQ(1U, nav_map->at(landing_url).size());
   ASSERT_EQ(1U, nav_map->at(download_url).size());
   ASSERT_EQ(1U, nav_map->at(initial_url).size());
   VerifyNavigationEvent(GURL(),       // source_url
                         GURL(),       // source_main_frame_url
                         initial_url,  // original_request_url
                         initial_url,  // destination_url
                         true,         // is_user_initiated,
                         true,         // has_committed
@@ skipping 18 matching lines @@
   VerifyNavigationEvent(landing_url,   // source_url
                         landing_url,   // source_main_frame_url
                         download_url,  // original_request_url
                         download_url,  // destination_url
                         true,          // is_user_initiated,
                         false,         // has_committed
                         false,         // has_server_redirect
                         nav_map->at(download_url).at(0));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
-  EXPECT_EQ(std::size_t(4), referrer_chain.size());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
+  EXPECT_EQ(4U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            landing_url,                       // referrer_url
                            landing_url,  // referrer_main_frame_url
                            false,        // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(landing_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            redirect_url,                      // referrer_url
                            redirect_url,  // referrer_main_frame_url
                            false,         // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
   VerifyReferrerChainEntry(redirect_url,                         // url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            test_server_ip,                       // ip_address
                            initial_url,                          // referrer_url
                            initial_url,  // referrer_main_frame_url
                            false,        // is_retargeting
-                           referrer_chain[2]);
+                           referrer_chain[2].get());
   VerifyReferrerChainEntry(
       initial_url,                           // url
       ReferrerChainEntry::LANDING_REFERRER,  // type
       test_server_ip,                        // ip_address
       GURL(),  // referrer_url is empty since this beyonds 2 clicks.
       GURL(),  // referrer_main_frame_url is empty for the same reason.
       false,   // is_retargeting
-      referrer_chain[3]);
+      referrer_chain[3].get());
 }
 
 // Click three links before reaching download.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
                        ReferrerAttributionWithinTwoUserGestures) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("attribution_within_two_user_gestures", 1, initial_url);
   GURL page_before_landing_referrer_url =
       embedded_test_server()->GetURL(kPageBeforeLandingReferrerURL);
   ClickTestLink("link_to_landing_referrer", 1,
                 page_before_landing_referrer_url);
   GURL landing_referrer_url =
       embedded_test_server()->GetURL(kLandingReferrerURL);
   ClickTestLink("link_to_landing", 1, landing_referrer_url);
   GURL landing_url = embedded_test_server()->GetURL(kLandingURL);
   ClickTestLink("download_on_landing_page", 1, landing_url);
   GURL download_url = embedded_test_server()->GetURL(kDownloadItemURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
   auto nav_map = navigation_map();
   ASSERT_TRUE(nav_map);
-  ASSERT_EQ(std::size_t(5), nav_map->size());
+  ASSERT_EQ(5U, nav_map->size());
   ASSERT_EQ(1U, nav_map->at(initial_url).size());
   ASSERT_EQ(1U, nav_map->at(page_before_landing_referrer_url).size());
   ASSERT_EQ(1U, nav_map->at(landing_referrer_url).size());
   ASSERT_EQ(1U, nav_map->at(landing_url).size());
   ASSERT_EQ(1U, nav_map->at(download_url).size());
   VerifyNavigationEvent(GURL(),       // source_url
                         GURL(),       // source_main_frame_url
                         initial_url,  // original_request_url
                         initial_url,  // destination_url
                         true,         // is_user_initiated,
@@ skipping 27 matching lines @@
   VerifyNavigationEvent(landing_url,   // source_url
                         landing_url,   // source_main_frame_url
                         download_url,  // original_request_url
                         download_url,  // destination_url
                         true,          // is_user_initiated,
                         false,         // has_committed
                         false,         // has_server_redirect
                         nav_map->at(download_url).at(0));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
-  EXPECT_EQ(std::size_t(3), referrer_chain.size());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
+  EXPECT_EQ(3U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            landing_url,                       // referrer_url
                            landing_url,  // referrer_main_frame_url
                            false,        // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(landing_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            landing_referrer_url,              // referrer_url
                            landing_referrer_url,  // referrer_main_frame_url
                            false,                 // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
   VerifyReferrerChainEntry(
       landing_referrer_url,                  // url
       ReferrerChainEntry::LANDING_REFERRER,  // type
       test_server_ip,                        // ip_address
       GURL(),  // referrer_url is empty since this beyonds 2 clicks.
       GURL(),  // referrer_main_frame_url is empty for the same reason.
       false,   // is_retargeting
-      referrer_chain[2]);
+      referrer_chain[2].get());
   // page_before_landing_referrer_url is not in referrer chain.
 }
 
 // Click a link which redirects to a PPAPI landing page.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
                        PPAPIDownloadWithUserGestureOnHostingFrame) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("complete_referrer_chain", 2, initial_url);
   GURL redirect_url = embedded_test_server()->GetURL(kRedirectToLandingURL);
   GURL landing_url = embedded_test_server()->GetURL(kLandingURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
 
   // Simulate a user gesture on landing page.
   SimulateUserGesture();
   auto nav_map = navigation_map();
   ASSERT_TRUE(nav_map);
-  ASSERT_EQ(std::size_t(3), nav_map->size());
+  ASSERT_EQ(3U, nav_map->size());
   ASSERT_EQ(1U, nav_map->at(redirect_url).size());
   ASSERT_EQ(1U, nav_map->at(landing_url).size());
   ASSERT_EQ(1U, nav_map->at(initial_url).size());
   VerifyNavigationEvent(GURL(),       // source_url
                         GURL(),       // source_main_frame_url
                         initial_url,  // original_request_url
                         initial_url,  // destination_url
                         true,         // is_user_initiated,
                         true,         // has_committed
                         false,        // has_server_redirect
                         nav_map->at(initial_url).at(0));
   VerifyNavigationEvent(initial_url,   // source_url
                         initial_url,   // source_main_frame_url
                         redirect_url,  // original_request_url
                         redirect_url,  // destination_url
                         true,          // is_user_initiated,
                         true,          // has_committed
                         false,         // has_server_redirect
                         nav_map->at(redirect_url).at(0));
   VerifyNavigationEvent(redirect_url,  // source_url
                         redirect_url,  // source_main_frame_url
                         landing_url,   // original_request_url
                         landing_url,   // destination_url
                         false,         // is_user_initiated,
                         true,          // has_committed
                         false,         // has_server_redirect
                         nav_map->at(landing_url).at(0));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForPPAPIDownload(
-      landing_url, browser()->tab_strip_model()->GetActiveWebContents());
-
-  EXPECT_EQ(std::size_t(3), referrer_chain.size());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForPPAPIDownload(
+      landing_url,
+      browser()->tab_strip_model()->GetActiveWebContents(),
+      &referrer_chain);
+  EXPECT_EQ(3U, referrer_chain.size());
   VerifyReferrerChainEntry(landing_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            redirect_url,                      // referrer_url
                            redirect_url,  // referrer_main_frame_url
                            false,         // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(redirect_url,                         // url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            test_server_ip,                       // ip_address
                            initial_url,                          // referrer_url
                            initial_url,  // referrer_main_frame_url
                            false,        // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
   VerifyReferrerChainEntry(
       initial_url,                           // url
       ReferrerChainEntry::LANDING_REFERRER,  // type
       test_server_ip,                        // ip_address
       GURL(),  // referrer_url is empty since this beyonds 2 clicks.
       GURL(),  // referrer_main_frame_url is empty for the same reason.
       false,   // is_retargeting
-      referrer_chain[2]);
+      referrer_chain[2].get());
 }
 
 // Click a link which redirects to a page that triggers PPAPI download without
 // user gesture (a.k.a not a landing page).
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
                        PPAPIDownloadWithoutUserGestureOnHostingFrame) {
   GURL landing_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   ClickTestLink("complete_referrer_chain", 2, landing_url);
   GURL redirect_url = embedded_test_server()->GetURL(kRedirectToLandingURL);
   GURL hosting_url = embedded_test_server()->GetURL(kLandingURL);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
 
   auto nav_map = navigation_map();
   ASSERT_TRUE(nav_map);
-  ASSERT_EQ(std::size_t(3), nav_map->size());
+  ASSERT_EQ(3U, nav_map->size());
   ASSERT_EQ(1U, nav_map->at(redirect_url).size());
   ASSERT_EQ(1U, nav_map->at(hosting_url).size());
   ASSERT_EQ(1U, nav_map->at(landing_url).size());
   VerifyNavigationEvent(GURL(),       // source_url
                         GURL(),       // source_main_frame_url
                         landing_url,  // original_request_url
                         landing_url,  // destination_url
                         true,         // is_user_initiated,
                         true,         // has_committed
                         false,        // has_server_redirect
                         nav_map->at(landing_url).at(0));
   VerifyNavigationEvent(landing_url,   // source_url
                         landing_url,   // source_main_frame_url
                         redirect_url,  // original_request_url
                         redirect_url,  // destination_url
                         true,          // is_user_initiated,
                         true,          // has_committed
                         false,         // has_server_redirect
                         nav_map->at(redirect_url).at(0));
   VerifyNavigationEvent(redirect_url,  // source_url
                         redirect_url,  // source_main_frame_url
                         hosting_url,   // original_request_url
                         hosting_url,   // destination_url
                         false,         // is_user_initiated,
                         true,          // has_committed
                         false,         // has_server_redirect
                         nav_map->at(hosting_url).at(0));
   VerifyHostToIpMap();
 
-  auto referrer_chain = IdentifyReferrerChainForPPAPIDownload(
-      hosting_url, browser()->tab_strip_model()->GetActiveWebContents());
-
-  EXPECT_EQ(std::size_t(3), referrer_chain.size());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForPPAPIDownload(
+      hosting_url,
+      browser()->tab_strip_model()->GetActiveWebContents(),
+      &referrer_chain);
+  EXPECT_EQ(3U, referrer_chain.size());
   VerifyReferrerChainEntry(hosting_url,                       // url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            test_server_ip,                    // ip_address
                            redirect_url,                      // referrer_url
                            redirect_url,  // referrer_main_frame_url
                            false,         // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(redirect_url,                         // url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            test_server_ip,                       // ip_address
                            landing_url,                          // referrer_url
                            landing_url,  // referrer_main_frame_url
                            false,        // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
   VerifyReferrerChainEntry(landing_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),  // no more referrer before landing_url
                            GURL(),
                            false,   // is_retargeting
-                           referrer_chain[2]);
+                           referrer_chain[2].get());
 }
 
 // Server-side redirect.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest, ServerRedirect) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   GURL download_url = embedded_test_server()->GetURL(kDownloadItemURL);
   GURL request_url =
       embedded_test_server()->GetURL("/server-redirect?" + download_url.spec());
   ui_test_utils::NavigateToURL(browser(), request_url);
   std::string test_server_ip(embedded_test_server()->host_port_pair().host());
@@ skipping 12 matching lines @@
                         nav_map->at(initial_url).at(0));
   VerifyNavigationEvent(GURL(),        // source_url
                         GURL(),        // source_main_frame_url
                         request_url,   // original_request_url
                         download_url,  // destination_url
                         true,          // is_user_initiated,
                         false,         // has_committed
                         true,          // has_server_redirect
                         nav_map->at(download_url).at(0));
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
   ASSERT_EQ(1U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,   // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
 }
 
 // Retargeting immediately followed by server-side redirect.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest,
                        RetargetingAndServerRedirect) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   GURL download_url = embedded_test_server()->GetURL(kDownloadItemURL);
   GURL request_url =
       embedded_test_server()->GetURL("/server-redirect?" + download_url.spec());
   ClickTestLink("new_tab_download_with_server_redirect", 1, initial_url);
@@ skipping 22 matching lines @@
                         nav_map->at(request_url).at(0));
   VerifyNavigationEvent(GURL(),        // source_url
                         GURL(),        // source_main_frame_url
                         request_url,   // original_request_url
                         download_url,  // destination_url
                         false,          // is_user_initiated,
                         false,         // has_committed
                         true,          // has_server_redirect
                         nav_map->at(download_url).at(0));
 
-  auto referrer_chain = IdentifyReferrerChainForDownload(GetDownload());
+  ReferrerChain referrer_chain;
+  IdentifyReferrerChainForDownload(GetDownload(), &referrer_chain);
   ASSERT_EQ(2U, referrer_chain.size());
   VerifyReferrerChainEntry(download_url,                      // url
                            ReferrerChainEntry::DOWNLOAD_URL,  // type
                            test_server_ip,                    // ip_address
                            initial_url,                       // referrer_url
                            initial_url,  // referrer_main_frame_url
                            true,         // is_retargeting
-                           referrer_chain[0]);
+                           referrer_chain[0].get());
   VerifyReferrerChainEntry(initial_url,                       // url
                            ReferrerChainEntry::LANDING_PAGE,  // type
                            test_server_ip,                    // ip_address
                            GURL(),                            // referrer_url
                            GURL(),  // referrer_main_frame_url
                            false,   // is_retargeting
-                           referrer_chain[1]);
+                           referrer_chain[1].get());
 }
 
 // host_to_ip_map_ size should increase by one after a new navigation.
 IN_PROC_BROWSER_TEST_F(SBNavigationObserverBrowserTest, AddIPMapping) {
   GURL initial_url = embedded_test_server()->GetURL(kSingleFrameTestURL);
   auto ip_map = host_to_ip_map();
   std::string test_server_host(embedded_test_server()->base_url().host());
   ip_map->clear();
   ip_map->insert(
       std::make_pair(test_server_host, std::vector<ResolvedIPAddress>()));
@@ skipping 18 matching lines @@
           yesterday, embedded_test_server()->host_port_pair().host()));
   ASSERT_EQ(1U, ip_map->at(test_server_host).size());
   ClickTestLink("direct_download", 1, initial_url);
   EXPECT_EQ(1U, ip_map->at(test_server_host).size());
   EXPECT_EQ(embedded_test_server()->host_port_pair().host(),
             ip_map->at(test_server_host).back().ip);
   EXPECT_NE(yesterday, ip_map->at(test_server_host).front().timestamp);
 }
 
 }  // namespace safe_browsing