Add a browsertest suite for net predictor

chrome/browser/net/predictor_browsertest.cc

Index: chrome/browser/net/predictor_browsertest.cc
diff --git a/chrome/browser/net/predictor_browsertest.cc b/chrome/browser/net/predictor_browsertest.cc
index 0b1884856d51aaa37ca2f5757b48499e2ff05839..5fe2eb38e550c550efbcc8b47a3f690b59e58313 100644
--- a/chrome/browser/net/predictor_browsertest.cc
+++ b/chrome/browser/net/predictor_browsertest.cc
@@ -16,11 +16,13 @@
 #include "chrome/browser/net/predictor.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/browser.h"
+#include "chrome/browser/ui/tabs/tab_strip_model.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/test/base/in_process_browser_test.h"
 #include "chrome/test/base/ui_test_utils.h"
 #include "components/prefs/pref_service.h"
 #include "content/public/common/content_switches.h"
+#include "content/public/test/browser_test_utils.h"
 #include "content/public/test/test_utils.h"
 #include "net/base/host_port_pair.h"
 #include "net/base/ip_endpoint.h"
@@ -30,6 +32,11 @@
 #include "net/socket/stream_socket.h"
 #include "net/test/embedded_test_server/embedded_test_server.h"
 #include "net/test/embedded_test_server/embedded_test_server_connection_listener.h"
+#include "net/test/embedded_test_server/http_request.h"
+#include "net/test/embedded_test_server/http_response.h"
+#include "net/test/url_request/url_request_failed_job.h"
+#include "net/url_request/url_request_filter.h"
+#include "net/url_request/url_request_interceptor.h"
 #include "testing/gmock/include/gmock/gmock.h"
 
 using content::BrowserThread;
@@ -71,7 +78,11 @@ class ConnectionListener
 
   // Get called from the EmbeddedTestServer thread to be notified that
   // a connection was read from.
-  void ReadFromSocket(const net::StreamSocket& connection) override {
+  void ReadFromSocket(const net::StreamSocket& connection, int rv) override {
+    // Don't log a read if no data was transferred. This case often happens if
+    // the sockets of the test server are being flushed and disconnected.
+    if (rv <= 0)
+      return;
     base::AutoLock lock(lock_);
     uint16_t socket = GetPort(connection);
     EXPECT_FALSE(sockets_.find(socket) == sockets_.end());
@@ -101,6 +112,11 @@ class ConnectionListener
 
   void WaitUntilFirstConnectionRead() { read_loop_.Run(); }
 
+  void ClearSockets() {

[mmenke, 2016/04/22 16:29:26]

ClearSocketCounts?  The external API is all about socket counts, tracking
sockets themselves is more of an implementation detail.

[Charlie Harrison, 2016/04/28 16:29:51]

Done.

+    base::AutoLock lock(lock_);
+    sockets_.clear();
+  }
+
  private:
   static uint16_t GetPort(const net::StreamSocket& connection) {
     // Get the remote port of the peer, since the local port will always be the
@@ -202,6 +218,111 @@ class HostResolutionRequestRecorder : public net::HostResolverProc {
   DISALLOW_COPY_AND_ASSIGN(HostResolutionRequestRecorder);
 };
 
+// This class intercepts URLRequests and responds with 404s.
+class NotFoundRequestInterceptor : public net::URLRequestInterceptor {
+ public:
+  NotFoundRequestInterceptor() {}
+  ~NotFoundRequestInterceptor() override {}
+
+ private:
+  net::URLRequestJob* MaybeInterceptRequest(
+      net::URLRequest* request,
+      net::NetworkDelegate* network_delegate) const override {
+    const char kHeaders[] =
+        "HTTP/1.1 404 Not Found\n"
+        "\n";
+    std::string headers(kHeaders, arraysize(kHeaders));

[mmenke, 2016/04/22 16:29:25]

Above two lines aren't used.

[Charlie Harrison, 2016/04/28 16:29:51]

Done.

+
+    return new net::URLRequestFailedJob(request, network_delegate,
+                                        net::ERR_ABORTED);
+  }
+  DISALLOW_COPY_AND_ASSIGN(NotFoundRequestInterceptor);
+};
+
+class CrossSitePredictorObserver
+    : public chrome_browser_net::PredictorObserver {
+ public:
+  CrossSitePredictorObserver(const GURL source_host, const GURL cross_site_host)

[mmenke, 2016/04/22 16:29:25]

nit:  const GURL& (x2)

[mmenke, 2016/04/22 16:29:25]

include gurl.h

[Charlie Harrison, 2016/04/28 16:29:51]

Done.

[Charlie Harrison, 2016/04/28 16:29:51]

Done.

+      : source_host_(source_host),
+        cross_site_host_(cross_site_host),
+        cross_site_learned_(0),
+        same_site_learned_(0),

[mmenke, 2016/04/22 16:29:25]

I don't think we ever use same_site_learned_?  The cookie requests make it
inherently racy, unless we always wait for them.

[Charlie Harrison, 2016/04/28 16:29:51]

Removed. If we want to add tests for them we can later.

+        cross_site_preconnected_(0),
+        same_site_preconnected_(0) {}
+
+  void OnPreconnectUrl(
+      const GURL& original_url,
+      const GURL& first_party_for_cookies,
+      chrome_browser_net::UrlInfo::ResolutionMotivation motivation,
+      int count) override {
+    base::AutoLock lock(lock_);
+    if (original_url == cross_site_host_) {
+      cross_site_preconnected_ = std::max(cross_site_preconnected_, count);
+    } else if (original_url == source_host_) {
+      same_site_preconnected_ = std::max(same_site_preconnected_, count);
+    } else {
+      NOTREACHED() << "Preconnected" << original_url

[mmenke, 2016/04/22 16:29:25]

Should use ADD_FAILURE() instead (A gtest macro that's similar to
EXPECT_TRUE(false), instead of something similar to DCHECK(false))

[Charlie Harrison, 2016/04/28 16:29:51]

Done.

+                   << " When should only be preconnecting the source host: "
+                   << source_host_
+                   << " or the cross site host: " << cross_site_host_;
+    }
+  }
+
+  void OnLearnFromNavigation(const GURL& referring_url,
+                             const GURL& target_url) override {
+    base::AutoLock lock(lock_);
+    if (referring_url == source_host_ && target_url == cross_site_host_) {
+      cross_site_learned_++;
+    } else if (referring_url == source_host_ && target_url == source_host_) {
+      same_site_learned_++;
+    } else if (referring_url != cross_site_host_) {

[mmenke, 2016/04/22 16:29:25]

What if target_url is unexpected?  Can we just do:

else if (referring_url != cross_site_host_ || (target_url == cross_site_host_ &&
target_url == source_host_))

Or maybe simpler, get rid of the else, and check if either URL is unexpected. 
We also don't expect cross_site_host_ to have a target URL of source_host_, do
we?

[Charlie Harrison, 2016/04/28 16:29:51]

The code in your comment is a bit unclear but I think I get your gist.
There are three possibilities:
source => target
source => source
target => target

I've updated the if statement to reference these states, hopefully making it a
bit more clear.

+      NOTREACHED() << "Learned " << referring_url << " => " << target_url

[mmenke, 2016/04/22 16:29:25]

ADD_FAILURE()

[Charlie Harrison, 2016/04/28 16:29:51]

Done.

+                   << " When should only be learning the source host: "
+                   << source_host_
+                   << " or the cross site host: " << cross_site_host_;
+    }
+  }
+
+  void ResetCounts() {
+    base::AutoLock lock(lock_);
+    cross_site_learned_ = 0;
+    same_site_learned_ = 0;
+    cross_site_preconnected_ = 0;
+    same_site_preconnected_ = 0;
+  }
+
+  int cross_site_learned() const {
+    base::AutoLock lock(lock_);
+    return cross_site_learned_;
+  }
+
+  int same_site_learned() const {
+    base::AutoLock lock(lock_);
+    return same_site_learned_;
+  }
+
+  int cross_site_preconnected() const {
+    base::AutoLock lock(lock_);
+    return cross_site_preconnected_;
+  }
+
+  int same_site_preconnected() const {
+    base::AutoLock lock(lock_);
+    return same_site_preconnected_;
+  }
+
+ private:
+  const GURL source_host_;
+  const GURL cross_site_host_;
+
+  int cross_site_learned_;
+  int same_site_learned_;
+
+  int cross_site_preconnected_;
+  int same_site_preconnected_;
+  mutable base::Lock lock_;

[mmenke, 2016/04/22 16:29:25]

DISALLOW_COPY_AND_ASSIGN

[Charlie Harrison, 2016/04/28 16:29:51]

Done.

+};
+
 }  // namespace
 
 namespace chrome_browser_net {
@@ -212,8 +333,8 @@ class PredictorBrowserTest : public InProcessBrowserTest {
       : startup_url_("http://host1:1"),
         referring_url_("http://host2:1"),
         target_url_("http://host3:1"),
-        host_resolution_request_recorder_(new HostResolutionRequestRecorder) {
-  }
+        host_resolution_request_recorder_(new HostResolutionRequestRecorder),
+        cross_site_test_server_(new net::EmbeddedTestServer()) {}
 
  protected:
   void SetUpInProcessBrowserTestFixture() override {
@@ -229,10 +350,43 @@ class PredictorBrowserTest : public InProcessBrowserTest {
         switches::kEnableBlinkFeatures, kBlinkPreconnectFeature);
   }
 
+  std::unique_ptr<net::test_server::HttpResponse> HandleRequest(

[mmenke, 2016/04/22 16:29:25]

This method name should be clearer, and may need a comment.

[Charlie Harrison, 2016/04/28 16:29:52]

Updated the name to "RedirectForPathPathHandler".

+      const net::test_server::HttpRequest& request) {
+    if (request.GetURL().path() != "/")

[mmenke, 2016/04/22 16:29:25]

Suggest taking this as an argument, then can have a better description of just
what's doing on in the RegisterRequestHandler line, and think the code will be a
little clearer.

[Charlie Harrison, 2016/04/28 16:29:52]

Done.

+      return nullptr;
+    std::unique_ptr<net::test_server::BasicHttpResponse> response(
+        new net::test_server::BasicHttpResponse);
+    response->set_code(net::HTTP_MOVED_PERMANENTLY);
+    response->AddCustomHeader(
+        "Location", cross_site_test_server()->GetURL("/title1.html").spec());

[mmenke, 2016/04/22 16:29:25]

Calling into the cross_site_test_server on the other test server's thread makes
me nervous.  Can we just make this method static, and pass in the GURL?  We will
need to start the cross_site_test_server before we register this handler, but
not a big deal, I think.

[Charlie Harrison, 2016/04/28 16:29:52]

Done.

+    return std::move(response);
+  }
+
   void SetUpOnMainThread() override {
+    embedded_test_server()->RegisterRequestHandler(base::Bind(
+        &PredictorBrowserTest::HandleRequest, base::Unretained(this)));
+    cross_site_test_server_->ServeFilesFromSourceDirectory("chrome/test/data/");
+
     connection_listener_.reset(new ConnectionListener());
+    cross_site_connection_listener_.reset(new ConnectionListener());
     embedded_test_server()->SetConnectionListener(connection_listener_.get());
+    cross_site_test_server_->SetConnectionListener(
+        cross_site_connection_listener_.get());
     ASSERT_TRUE(embedded_test_server()->Start());
+    ASSERT_TRUE(cross_site_test_server_->Start());
+
+    predictor()->set_preconnect_enabled_for_test(true);
+    BrowserThread::PostTask(BrowserThread::IO, FROM_HERE,
+                            base::Bind(&PredictorBrowserTest::SetUpOnIOThread,
+                                       base::Unretained(this)));
+  }
+
+  void SetUpOnIOThread() {
+    // Ignore all favicon requests. These are tricky to deal with because they
+    // are scheduled on the UI thread and are not accounted for in the load
+    // event. The interceptor will respond with 404s, and won't connect any
+    // sockets to the test server.
+    AddUrlInterceptor(cross_site_test_server()->GetURL("/favicon.ico"));
   }
 
   void TearDownOnMainThread() override {
@@ -254,29 +408,22 @@ class PredictorBrowserTest : public InProcessBrowserTest {
   }
 
   void LearnAboutInitialNavigation(const GURL& url) {
-    Predictor* predictor = browser()->profile()->GetNetworkPredictor();
-    BrowserThread::PostTask(BrowserThread::IO,
-                            FROM_HERE,
+    BrowserThread::PostTask(BrowserThread::IO, FROM_HERE,
                             base::Bind(&Predictor::LearnAboutInitialNavigation,
-                                       base::Unretained(predictor),
-                                       url));
+                                       base::Unretained(predictor()), url));
     content::RunAllPendingInMessageLoop(BrowserThread::IO);
   }
 
   void LearnFromNavigation(const GURL& referring_url, const GURL& target_url) {
-    Predictor* predictor = browser()->profile()->GetNetworkPredictor();
-    BrowserThread::PostTask(BrowserThread::IO,
-                            FROM_HERE,
-                            base::Bind(&Predictor::LearnFromNavigation,
-                                       base::Unretained(predictor),
-                                       referring_url,
-                                       target_url));
+    BrowserThread::PostTask(
+        BrowserThread::IO, FROM_HERE,
+        base::Bind(&Predictor::LearnFromNavigation,
+                   base::Unretained(predictor()), referring_url, target_url));
     content::RunAllPendingInMessageLoop(BrowserThread::IO);
   }
 
   void PrepareFrameSubresources(const GURL& url) {
-    Predictor* predictor = browser()->profile()->GetNetworkPredictor();
-    predictor->PredictFrameSubresources(url, GURL());
+    predictor()->PredictFrameSubresources(url, GURL());
   }
 
   void GetListFromPrefsAsString(const char* list_path,
@@ -299,26 +446,431 @@ class PredictorBrowserTest : public InProcessBrowserTest {
     return host_resolution_request_recorder_->RequestedHostnameCount();
   }
 
+  net::EmbeddedTestServer* cross_site_test_server() {
+    return cross_site_test_server_.get();
+  }
+
+  Predictor* predictor() { return browser()->profile()->GetNetworkPredictor(); }
+
+  void InstallPredictorObserver() {
+    BrowserThread::PostTask(
+        BrowserThread::IO, FROM_HERE,
+        base::Bind(&PredictorBrowserTest::InstallPredictorObserverOnIOThread,
+                   base::Unretained(this), base::Unretained(predictor())));
+  }
+
+  void InstallPredictorObserverOnIOThread(
+      chrome_browser_net::Predictor* predictor) {
+    observer_.reset(
+        new CrossSitePredictorObserver(embedded_test_server()->base_url(),
+                                       cross_site_test_server()->base_url()));

[mmenke, 2016/04/22 16:29:25]

Suggest just creating the observer_ in InstallPredictorObserver.  Otherwise,
have to reason about whether it's guaranteed to have been created before
accessing it on the UI thread.

[Charlie Harrison, 2016/04/28 16:29:51]

Done.

+    predictor->SetObserver(observer_.get());
+  }
+
+  CrossSitePredictorObserver* observer() { return observer_.get(); }
+
+  // Navigate to an html file and request async fetches. Wait until the fetches

[mmenke, 2016/04/22 16:29:25]

Suggest "Navigate to an html file and request async fetches" -> "Navigate to an
html file on embedded_test_server and tell it to request |num_cors| |num_cors|
resources from the cross_site_test_server.  Then waits for those requests to
complete."

[Charlie Harrison, 2016/04/28 16:29:51]

Done.

+  // complete before continuing. Note that "cors" here means using cors-mode in
+  // correspondence with the fetch spec. This translates to using the privacy
+  // mode socket pools.
+  void NavigateToCrossSiteHTMLURL(int num_cors, const char* file_suffix) {
+    const GURL& base_url = cross_site_test_server()->base_url();
+    std::string path = base::StringPrintf(
+        "/predictor/"
+        "predictor_cross_site%s.html?subresourceHost=%s&"
+        "numCORSResources=%d",
+        file_suffix, base_url.spec().c_str(), num_cors);
+    ui_test_utils::NavigateToURL(browser(),
+                                 embedded_test_server()->GetURL(path));
+    bool result = false;
+    EXPECT_TRUE(content::ExecuteScriptAndExtractBool(
+        browser()->tab_strip_model()->GetActiveWebContents(), "sendFetches()",

[mmenke, 2016/04/22 16:29:25]

Maybe sendFetches -> startFetchesAndWaitForReply?  Open to other ideas, just
want a name that makes it cleaerer this does more than send the requests.

[Charlie Harrison, 2016/04/28 16:29:51]

SGTM. Done.

+        &result));
+    EXPECT_TRUE(result);
+  }
+
+  // Simulate the target server restarting. Delete all sockets and reset members
+  // tracking preconnects.
+  void ResetTarget() {
+    cross_site_test_server()->FlushAllSocketsAndConnectionsOnUIThread();
+    cross_site_connection_listener_->ClearSockets();
+    EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  }
+
+  static void AddUrlInterceptor(const GURL url) {

[mmenke, 2016/04/22 16:29:25]

GURL&

[Charlie Harrison, 2016/04/28 16:29:51]

Done.

+    net::URLRequestFilter::GetInstance()->AddUrlInterceptor(
+        url, make_scoped_ptr(new NotFoundRequestInterceptor()));
+  }
+
   const GURL startup_url_;
   const GURL referring_url_;
   const GURL target_url_;
   std::unique_ptr<ConnectionListener> connection_listener_;
+  std::unique_ptr<ConnectionListener> cross_site_connection_listener_;
 
  private:
   scoped_refptr<HostResolutionRequestRecorder>
       host_resolution_request_recorder_;
   std::unique_ptr<net::ScopedDefaultHostResolverProc>
       scoped_host_resolver_proc_;
+  std::unique_ptr<net::EmbeddedTestServer> cross_site_test_server_;
+  std::unique_ptr<CrossSitePredictorObserver> observer_;
 };
 
-IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, PRE_ShutdownStartupCycle) {
+// Test the html test harness used to initiate cross site fetches. These
+// initiate cross site subresource requests to the cross site test server.
+// Inspect the predictor's internal state to make sure that they are properly
+// logged.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, CrossSiteUseOneSocket) {
+  InstallPredictorObserver();
+  NavigateToCrossSiteHTMLURL(1 /* num_cors */, "" /* file_suffix */);
+  EXPECT_EQ(1u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(1, observer()->cross_site_learned());
+  EXPECT_EQ(2, observer()->same_site_preconnected());
+}
+
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, CrossSiteUseThreeSockets) {
+  InstallPredictorObserver();
+  NavigateToCrossSiteHTMLURL(3 /* num_cors */, "" /* file_suffix */);
+  EXPECT_EQ(3u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(3, observer()->cross_site_learned());
+  EXPECT_EQ(2, observer()->same_site_preconnected());
+}
+
+// The following tests confirm that Chrome accurately predicts preconnects after
+// learning from navigations. Note that every "learned" connection adds ~.33 to
+// the expected connection number, which starts at 2. Every preconnect Chrome
+// performs multiplies the expected connections by .66. One additional
+// complexity
+// is that if a preconnect from A to B is learned, an extra preconnect will be
+// issued if the host part of A and B match (ignoring port).
+// TODO(csharrison): This logic could probably be removed.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest,
+                       CrossSiteSimplePredictionAfterOneNavigation) {
+  InstallPredictorObserver();
+  NavigateToCrossSiteHTMLURL(2 /* num_cors */, "" /* file_suffix */);
+  EXPECT_EQ(2u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(2, observer()->cross_site_learned());
+  EXPECT_EQ(2, observer()->same_site_preconnected());
+
+  ResetTarget();
+  observer()->ResetCounts();
+
+  // Navigate again and confirm a preconnect. Note that because the two
+  // embedded test servers have the same host_piece, an extra preconnect is
+  // issued. This results in ceil(2.66) + 1 = 4 preconnects.
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  EXPECT_EQ(4u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(4, observer()->cross_site_preconnected());
+}
+
+// Expect that the predictor correctly predicts subframe navigations.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, SubframeCrossSitePrediction) {
+  InstallPredictorObserver();
+  ui_test_utils::NavigateToURL(
+      browser(), embedded_test_server()->GetURL(
+                     "/predictor/predictor_cross_site_subframe_nav.html"));
+  bool result = false;
+  EXPECT_TRUE(content::ExecuteScriptAndExtractBool(
+      browser()->tab_strip_model()->GetActiveWebContents(),
+      base::StringPrintf(
+          "navigateSubframe('%s')",
+          cross_site_test_server()->GetURL("/title1.html").spec().c_str()),
+      &result));
+  EXPECT_TRUE(result);
+  EXPECT_EQ(2u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(1, observer()->cross_site_learned());
+  EXPECT_EQ(2, observer()->same_site_preconnected());
+
+  ResetTarget();
+  observer()->ResetCounts();
+
+  // Navigate again and confirm a preconnect. Note that because the two
+  // embedded test servers have the same host_piece, an extra preconnect is
+  // issued. This results in ceil(2 + .33) + 1 = 4 preconnects.
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  EXPECT_EQ(4u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(4, observer()->cross_site_preconnected());
+}
+
+// Expect that the predictor correctly preconnects an already learned resource
+// if the host shows up in a subframe.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, SubframeInitiatesPreconnects) {
+  InstallPredictorObserver();
+  // Navigate to the normal cross site URL to learn the relationship.
+  NavigateToCrossSiteHTMLURL(1 /* num_cors */, "" /* file_suffix */);
+  EXPECT_EQ(1u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(1, observer()->cross_site_learned());
+  EXPECT_EQ(2, observer()->same_site_preconnected());
+
+  ResetTarget();
+  observer()->ResetCounts();
+
+  // Navigate again and confirm a preconnect. Note that because the two
+  // embedded test servers have the same host_piece, an extra preconnect is
+  // issued. This results in ceil(2 + .33) + 1 = 4 preconnects.
+  NavigateToDataURLWithContent(
+      "<iframe src=\"" + embedded_test_server()->GetURL("/title1.html").spec() +
+      "\"></iframe>");
+  EXPECT_EQ(4u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(4, observer()->cross_site_preconnected());
+}
+
+// Expect that the predictor correctly learns the subresources a subframe needs
+// to preconnect to.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, SubframeLearning) {
+  InstallPredictorObserver();
+  std::string path = base::StringPrintf(
+      "/predictor/"
+      "predictor_cross_site.html?subresourceHost=%s&"
+      "numCORSResources=1&sendImmediately=1",
+      cross_site_test_server()->base_url().spec().c_str());
+  NavigateToDataURLWithContent(
+      base::StringPrintf("<iframe src=\"%s\"></iframe>",
+                         embedded_test_server()->GetURL(path).spec().c_str()));
+  cross_site_connection_listener_->WaitUntilFirstConnectionRead();
+  EXPECT_EQ(1u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(1, observer()->cross_site_learned());
+  EXPECT_EQ(2, observer()->same_site_preconnected());
+
+  ResetTarget();
+  observer()->ResetCounts();
+
+  // Navigate again and confirm a preconnect. Note that because the two
+  // embedded test servers have the same host_piece, an extra preconnect is
+  // issued. This results in ceil(2 + .33) + 1 = 4 preconnects.
+  NavigateToDataURLWithContent(
+      "<iframe src=\"" + embedded_test_server()->GetURL("/title1.html").spec() +
+      "\"></iframe>");
+  EXPECT_EQ(4u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(4, observer()->cross_site_preconnected());
+}
+
+// This tests the implementation details of the predictor. The current predictor
+// only learns via the referrer header.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, CrossSiteNoReferrerNoLearning) {
+  InstallPredictorObserver();
+  NavigateToCrossSiteHTMLURL(1 /* num_cors */,
+                             "_no_referrer" /* file_suffix */);
+  EXPECT_EQ(1u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(0, observer()->cross_site_learned());
+  EXPECT_EQ(2, observer()->same_site_preconnected());
+}
+
+// This test navigates to an html file with a tag:
+// <meta name="referrer" content="never">
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest,
+                       CrossSiteNoReferrerNoPredictionAfterOneNavigation) {
+  InstallPredictorObserver();
+  NavigateToCrossSiteHTMLURL(2 /* num_cors */,
+                             "_no_referrer" /* file_suffix */);
+  EXPECT_EQ(2u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(0, observer()->cross_site_learned());
+  EXPECT_EQ(2, observer()->same_site_preconnected());
+
+  ResetTarget();
+  observer()->ResetCounts();
+
+  // Navigate again and confirm that no preconnects occurred.
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(0, observer()->cross_site_preconnected());
+}
+
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest,
+                       CrossSiteSimplePredictionAfterTwoNavigations) {
+  InstallPredictorObserver();
+  NavigateToCrossSiteHTMLURL(1 /* num_cors */, "" /* file_suffix */);
+  NavigateToCrossSiteHTMLURL(1 /* num_cors */, "" /* file_suffix */);
+
+  ResetTarget();
+  observer()->ResetCounts();
+
+  // Navigate again and confirm a preconnect. Note that because the two
+  // embedded test servers have the same host_piece, an extra preconnect is
+  // issued. This results in ceil((2 + .33)*.66 + .33) + 1 ~= 3 preconnects.
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  EXPECT_EQ(3u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(3, observer()->cross_site_preconnected());
+}
+
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest,
+                       CrossSiteSimplePredictionAfterTwoNavigations2) {
+  InstallPredictorObserver();
+  NavigateToCrossSiteHTMLURL(2 /* num_cors */, "" /* file_suffix */);
+  NavigateToCrossSiteHTMLURL(2 /* num_cors */, "" /* file_suffix */);
+
+  ResetTarget();
+  observer()->ResetCounts();
+
+  // (((2 + .66)*.66) + .66) + 1 ~= 3.4
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  EXPECT_EQ(4u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(4, observer()->cross_site_preconnected());
+}
+
+// The first navigation uses a subresource. Subsequent navigations don't use
+// that subresource. This tests how the predictor forgets about these bad
+// navigations.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, ForgetBadPrediction) {
+  InstallPredictorObserver();
+  NavigateToCrossSiteHTMLURL(1 /* num_cors */, "" /* file_suffix */);
+
+  ResetTarget();
+  observer()->ResetCounts();
+
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  // (2 + .33) + 1 = 3.33.
+  EXPECT_EQ(4u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(4, observer()->cross_site_preconnected());
+
+  ResetTarget();
+  observer()->ResetCounts();
+
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+
+  // ceil((2 + .33) * .66) + 1 = 3.
+  EXPECT_EQ(3u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(3, observer()->cross_site_preconnected());
+
+  ResetTarget();
+  observer()->ResetCounts();
+
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  // ceil((2 + .33) * .66 * .66) + 1 = 3.
+  EXPECT_EQ(3u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(3, observer()->cross_site_preconnected());
+
+  ResetTarget();
+  observer()->ResetCounts();
+
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  // Finally, (2 + .33) * .66^3 ~= .67. Not enough for a preconnect.
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(0, observer()->cross_site_preconnected());
+}
+
+// The predictor does not follow redirects if the original url had a non-empty
+// path (a path that was more than just "/").
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest,
+                       CrossSiteRedirectNoPredictionWithPath) {
+  InstallPredictorObserver();
+  ui_test_utils::NavigateToURL(
+      browser(),
+      embedded_test_server()->GetURL(base::StringPrintf(
+          "/server-redirect?%s",
+          cross_site_test_server()->GetURL("/title1.html").spec().c_str())));
+  EXPECT_EQ(2u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(0, observer()->cross_site_learned());
+  EXPECT_EQ(2, observer()->same_site_preconnected());
+
+  ResetTarget();
+  observer()->ResetCounts();
+
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(0, observer()->cross_site_preconnected());
+}
+
+// The predictor does follow redirects if the original url had an empty path
+// (a path that was more than just "/"). Use the registered "/" path to redirect
+// to the target test server.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest,
+                       CrossSiteRedirectPredictionWithNoPath) {
+  InstallPredictorObserver();
+  ui_test_utils::NavigateToURL(browser(), embedded_test_server()->GetURL("/"));
+  EXPECT_EQ(2u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(1, observer()->cross_site_learned());
+  EXPECT_EQ(2, observer()->same_site_preconnected());
+
+  ResetTarget();
+  observer()->ResetCounts();
+
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  // Preconnect 4 sockets because ceil(2 + .33) + 1 = 4.
+  EXPECT_EQ(4u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(4, observer()->cross_site_preconnected());
+}
+
+// This test uses "localhost" instead of "127.0.0.1" to avoid extra preconnects
+// to hosts with the same host piece (ignoring port). Note that the preconnect
+// observer is not used here due to its strict checks on hostname.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest,
+                       CrossSiteRedirectPredictionWithNoPathDifferentHostName) {
+  GURL localhost_source = GURL(base::StringPrintf(
+      "http://localhost:%s/predictor/"
+      "predictor_cross_site.html?subresourceHost=%s&numCORSResources=1",
+      embedded_test_server()->base_url().port().c_str(),
+      cross_site_test_server()->base_url().spec().c_str()));
+  ui_test_utils::NavigateToURL(browser(), localhost_source);
+  bool result = false;
+  EXPECT_TRUE(content::ExecuteScriptAndExtractBool(
+      browser()->tab_strip_model()->GetActiveWebContents(), "sendFetches()",
+      &result));
+  EXPECT_TRUE(result);
+
+  EXPECT_EQ(1u, cross_site_connection_listener_->GetAcceptedSocketCount());
+
+  ResetTarget();
+
+  ui_test_utils::NavigateToURL(
+      browser(), GURL(base::StringPrintf(
+                     "http://localhost:%s/title1.html",
+                     embedded_test_server()->base_url().port().c_str())));
+  // Preconnect 3 sockets because ceil(2 + .33) = 3. Note that this time there
+  // is no additional connection due to same host.
+  EXPECT_EQ(3u, cross_site_connection_listener_->GetAcceptedSocketCount());
+}
+
+// Perform the "/" redirect twice and make sure the predictor updates twice.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest,
+                       CrossSiteTwoRedirectsPredictionWithNoPath) {
+  InstallPredictorObserver();
+  ui_test_utils::NavigateToURL(browser(), embedded_test_server()->GetURL("/"));
+  EXPECT_EQ(1, observer()->cross_site_learned());
+  EXPECT_EQ(2, observer()->same_site_preconnected());
+
+  ui_test_utils::NavigateToURL(browser(), embedded_test_server()->GetURL("/"));
+  EXPECT_EQ(2, observer()->cross_site_learned());
+  EXPECT_EQ(2, observer()->same_site_preconnected());
+
+  ResetTarget();
+  observer()->ResetCounts();
+
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  // 3 preconnects expected because (2 + .33) * .66 + .33 + 1 ~= 2.87.
+  EXPECT_EQ(3u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(3, observer()->cross_site_preconnected());
+}
+
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest,
+                       PRE_ShutdownStartupCyclePreresolve) {
   // Prepare state that will be serialized on this shut-down and read on next
-  // start-up.
+  // start-up. Ensure preresolution over preconnection.
   LearnAboutInitialNavigation(startup_url_);
+  // The target url will have a expected connection count of 2 after this call.
   LearnFromNavigation(referring_url_, target_url_);
+
+  // In order to reduce the expected connection count < .8, issue predictions 3
+  // times. 2 * .66^3 ~= .58.
+  PrepareFrameSubresources(referring_url_);
+  PrepareFrameSubresources(referring_url_);
+  PrepareFrameSubresources(referring_url_);
 }
 
-IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, ShutdownStartupCycle) {
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, ShutdownStartupCyclePreresolve) {
   // Make sure that the Preferences file is actually wiped of all DNS prefetch
   // related data after start-up.
   std::string cleared_startup_list;