Clean up DownloadAttribution Finch experiments

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 145 matching lines @@
   std::vector<SafeBrowsingNavigationObserver*> observer_list_;
 
   content::NotificationRegistrar registrar_;
 };
 
 class SBNavigationObserverBrowserTest : public InProcessBrowserTest {
  public:
   SBNavigationObserverBrowserTest() {}
 
   void SetUpOnMainThread() override {
-    // Disable Safe Browsing service since it is irrelevant to this test.
+    // Disable Safe Browsing service so we can directly control when
+    // SafeBrowsingNavigationObserverManager and SafeBrowsingNavigationObserver
+    // are instantiated.
     browser()->profile()->GetPrefs()->SetBoolean(prefs::kSafeBrowsingEnabled,
                                                  false);
     ASSERT_TRUE(embedded_test_server()->Start());
     host_resolver()->AddRule("*", "127.0.0.1");
     observer_manager_ = new TestNavigationObserverManager();
     observer_ = new SafeBrowsingNavigationObserver(
         browser()->tab_strip_model()->GetActiveWebContents(),
         observer_manager_);
     ASSERT_TRUE(observer_);
     ASSERT_TRUE(InitialSetup());
@@ skipping 1782 matching lines @@
                            GURL(),       // main_frame_url
                            ReferrerChainEntry::CLIENT_REDIRECT,  // type
                            test_server_ip,                       // ip_address
                            GURL(),                               // referrer_url
                            GURL(),               // referrer_main_frame_url
                            false,                // is_retargeting
                            std::vector<GURL>(),  // server redirects
                            referrer_chain.Get(0));
 }
 }  // namespace safe_browsing