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 9ce80b59cf83455a86c9375994131ac7bc98df8c..5ddbd98e672e1470310e21e3d269c91e253d3f3d 100644
--- a/chrome/browser/net/predictor_browsertest.cc
+++ b/chrome/browser/net/predictor_browsertest.cc
@@ -5,10 +5,17 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include <algorithm>
+#include <memory>
+
 #include "base/base64.h"
+#include "base/bind.h"
+#include "base/callback.h"
 #include "base/command_line.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/macros.h"
+#include "base/memory/ptr_util.h"
+#include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "build/build_config.h"
@@ -16,27 +23,65 @@
 #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"
 #include "net/base/net_errors.h"
 #include "net/dns/host_resolver_proc.h"
 #include "net/dns/mock_host_resolver.h"
+#include "net/http/http_transaction_factory.h"
 #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_context.h"
+#include "net/url_request/url_request_context_getter.h"
+#include "net/url_request/url_request_filter.h"
+#include "net/url_request/url_request_interceptor.h"
+#include "net/url_request/url_request_test_job.h"
 #include "testing/gmock/include/gmock/gmock.h"
+#include "url/gurl.h"
 
 using content::BrowserThread;
 using testing::HasSubstr;
 
 namespace {
 
+net::URLRequestJob* CreateEmptyBodyRequestJob(net::URLRequest* request,
+                                              net::NetworkDelegate* delegate) {
+  const char kPlainTextHeaders[] =
+      "HTTP/1.1 200 OK\n"
+      "Content-Type: text/plain\n"
+      "Access-Control-Allow-Origin: *\n"
+      "\n";
+  return new net::URLRequestTestJob(request, delegate, kPlainTextHeaders, "",
+                                    true);
+}
+
+// Override the test server to redirect requests matching some path. This is
+// used because the predictor only learns simple redirects with a path of "/"
+std::unique_ptr<net::test_server::HttpResponse> RedirectForPathHandler(
+    const std::string& path,
+    const GURL& redirect_url,
+    const net::test_server::HttpRequest& request) {
+  if (request.GetURL().path() != path)
+    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", redirect_url.spec());
+  return std::move(response);
+}
+
 const char kBlinkPreconnectFeature[] = "LinkPreconnect";
 const char kChromiumHostname[] = "chromium.org";
 const char kInvalidLongHostname[] = "illegally-long-hostname-over-255-"
@@ -54,7 +99,10 @@ const char kInvalidLongHostname[] = "illegally-long-hostname-over-255-"
 class ConnectionListener
     : public net::test_server::EmbeddedTestServerConnectionListener {
  public:
-  ConnectionListener() : task_runner_(base::ThreadTaskRunnerHandle::Get()) {}
+  ConnectionListener()
+      : task_runner_(base::ThreadTaskRunnerHandle::Get()),
+        num_accepted_connections_needed_(0),
+        num_accepted_connections_loop_(nullptr) {}
 
   ~ConnectionListener() override {}
 
@@ -67,11 +115,16 @@ class ConnectionListener
 
     sockets_[socket] = SOCKET_ACCEPTED;
     task_runner_->PostTask(FROM_HERE, accept_loop_.QuitClosure());
+    CheckAccepted();
   }
 
   // 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());
@@ -98,9 +151,63 @@ class ConnectionListener
   }
 
   void WaitUntilFirstConnectionAccepted() { accept_loop_.Run(); }
-
   void WaitUntilFirstConnectionRead() { read_loop_.Run(); }
 
+  // The UI thread will wait for exactly |n| items in |sockets_|. |n| must be
+  // greater than 0.
+  void WaitForAcceptedConnectionsOnUI(size_t num_connections) {
+    DCHECK_CURRENTLY_ON(BrowserThread::UI);
+    DCHECK(!num_accepted_connections_loop_);
+    DCHECK_GT(num_connections, 0u);
+    base::RunLoop run_loop;
+    {
+      base::AutoLock lock(lock_);
+      EXPECT_GE(num_connections, sockets_.size());
+      num_accepted_connections_loop_ = &run_loop;
+      num_accepted_connections_needed_ = num_connections;
+      CheckAccepted();
+    }
+    // Note that the previous call to CheckAccepted can quit this run loop
+    // before this call, which will make this call a no-op.
+    run_loop.Run();
+
+    // Grab the mutex again and make sure that the number of accepted sockets is
+    // indeed |num_connections|.
+    base::AutoLock lock(lock_);
+    EXPECT_EQ(num_connections, sockets_.size());
+  }
+
+  void CheckAcceptedLocked() {
+    base::AutoLock lock(lock_);
+    CheckAccepted();
+  }
+
+  // Helper function to stop the waiting for sockets to be accepted for
+  // WaitForAcceptedConnectionsOnUI. |num_accepted_connections_loop_| spins
+  // until |num_accepted_connections_needed_| sockets are accepted by the test
+  // server. The values will be null/0 if the loop is not running.
+  void CheckAccepted() {
+    lock_.AssertAcquired();
+    // |num_accepted_connections_loop_| null implies
+    // |num_accepted_connections_needed_| == 0.
+    DCHECK(num_accepted_connections_loop_ ||
+           num_accepted_connections_needed_ == 0);
+    if (!num_accepted_connections_loop_ ||
+        num_accepted_connections_needed_ != sockets_.size()) {
+      return;
+    }
+
+    task_runner_->PostTask(FROM_HERE,
+                           num_accepted_connections_loop_->QuitClosure());
+    num_accepted_connections_needed_ = 0;
+    num_accepted_connections_loop_ = nullptr;
+  }
+
+  void ResetCounts() {
+    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
@@ -118,14 +225,22 @@ class ConnectionListener
 
   enum SocketStatus { SOCKET_ACCEPTED, SOCKET_READ_FROM };
 
-  typedef base::hash_map<uint16_t, SocketStatus> SocketContainer;
-  SocketContainer sockets_;
-
   base::RunLoop accept_loop_;
   base::RunLoop read_loop_;
+
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
 
+  // This lock protects all the members below, which each are used on both the
+  // IO and UI thread. Members declared after the lock are protected by it.
   mutable base::Lock lock_;
+  typedef base::hash_map<uint16_t, SocketStatus> SocketContainer;
+  SocketContainer sockets_;
+
+  // If |num_accepted_connections_needed_| is non zero, then the object is
+  // waiting for |num_accepted_connections_needed_| sockets to be accepted
+  // before quitting the |num_accepted_connections_loop_|.
+  size_t num_accepted_connections_needed_;
+  base::RunLoop* num_accepted_connections_loop_;
 
   DISALLOW_COPY_AND_ASSIGN(ConnectionListener);
 };
@@ -202,6 +317,128 @@ class HostResolutionRequestRecorder : public net::HostResolverProc {
   DISALLOW_COPY_AND_ASSIGN(HostResolutionRequestRecorder);
 };
 
+// This class intercepts URLRequests and responds with the URLRequestJob*
+// callback provided by the constructor. Note that the port of the URL must
+// match the port given in the constructor.
+class MatchingPortRequestInterceptor : public net::URLRequestInterceptor {
+ public:
+  typedef base::Callback<net::URLRequestJob*(net::URLRequest*,
+                                             net::NetworkDelegate*)>
+      CreateJobCallback;
+
+  MatchingPortRequestInterceptor(
+      int port,
+      base::Callback<net::URLRequestJob*(net::URLRequest*,
+                                         net::NetworkDelegate*)>
+          create_job_callback)
+      : create_job_callback_(create_job_callback), port_(port) {}
+  ~MatchingPortRequestInterceptor() override {}
+
+ private:
+  net::URLRequestJob* MaybeInterceptRequest(
+      net::URLRequest* request,
+      net::NetworkDelegate* network_delegate) const override {
+    if (request->url().EffectiveIntPort() != port_)
+      return nullptr;
+    return create_job_callback_.Run(request, network_delegate);
+  }
+
+  const CreateJobCallback create_job_callback_;
+  const int port_;
+
+  DISALLOW_COPY_AND_ASSIGN(MatchingPortRequestInterceptor);
+};
+
+// This class is owned by the test harness, and listens to Predictor events. It
+// takes as input the source host and cross site host used by the test harness,
+// and asserts that only valid preconnects and learning can occur between the
+// two.
+class CrossSitePredictorObserver
+    : public chrome_browser_net::PredictorObserver {
+ public:
+  CrossSitePredictorObserver(const GURL& source_host,
+                             const GURL& cross_site_host)
+      : source_host_(source_host),
+        cross_site_host_(cross_site_host),
+        cross_site_learned_(0),
+        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 {
+      ADD_FAILURE() << "Preconnected " << original_url
+                    << " 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_);
+    // There are three possibilities:
+    //     source => target
+    //     source => source
+    //     target => target
+    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. Branch retained for clarity.
+    } else if (!(referring_url == cross_site_host_ &&
+                 target_url == cross_site_host_)) {
+      ADD_FAILURE() << "Learned " << referring_url << " => " << target_url
+                    << " 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;
+    cross_site_preconnected_ = 0;
+    same_site_preconnected_ = 0;
+  }
+
+  int CrossSiteLearned() {
+    base::AutoLock lock(lock_);
+    return cross_site_learned_;
+  }
+
+  int CrossSitePreconnected() {
+    base::AutoLock lock(lock_);
+    return cross_site_preconnected_;
+  }
+
+  int SameSitePreconnected() {
+    base::AutoLock lock(lock_);
+    return same_site_preconnected_;
+  }
+
+ private:
+  const GURL source_host_;
+  const GURL cross_site_host_;
+
+  // Protects all following members. They are read and updated from different
+  // threads.
+  base::Lock lock_;
+
+  int cross_site_learned_;
+  int cross_site_preconnected_;
+  int same_site_preconnected_;
+
+  DISALLOW_COPY_AND_ASSIGN(CrossSitePredictorObserver);
+};
+
 }  // namespace
 
 namespace chrome_browser_net {
@@ -212,8 +449,8 @@ 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 {
@@ -230,18 +467,72 @@ class PredictorBrowserTest : public InProcessBrowserTest {
   }
 
   void SetUpOnMainThread() override {
+    DCHECK_CURRENTLY_ON(BrowserThread::UI);
+    task_runner_ = base::ThreadTaskRunnerHandle::Get();
+    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());
+
+    embedded_test_server()->RegisterRequestHandler(
+        base::Bind(&RedirectForPathHandler, "/",
+                   cross_site_test_server()->GetURL("/title1.html")));
+
+    predictor()->SetPreconnectEnabledForTest(true);
+    InstallPredictorObserver(embedded_test_server()->base_url(),
+                             cross_site_test_server()->base_url());
+    StartInterceptingCrossSiteOnUI();
+  }
+
+  // Intercepts all requests to the specified host and returns a response with
+  // an empty body. Needed to prevent requests from actually going to the test
+  // server, to avoid any races related to socket accounting. Note, the
+  // interceptor also looks at the port, to differentiate between the
+  // two test servers.
+  static void StartInterceptingHost(const GURL& url) {
+    DCHECK_CURRENTLY_ON(BrowserThread::IO);
+    net::URLRequestFilter::GetInstance()->AddHostnameInterceptor(
+        url.scheme(), url.host(),
+        base::WrapUnique(new MatchingPortRequestInterceptor(
+            url.EffectiveIntPort(), base::Bind(&CreateEmptyBodyRequestJob))));
+  }
+
+  static void StopInterceptingHost(const GURL& url) {
+    DCHECK_CURRENTLY_ON(BrowserThread::IO);
+    net::URLRequestFilter::GetInstance()->RemoveHostnameHandler(url.scheme(),
+                                                                url.host());
+  }
+
+  void StartInterceptingCrossSiteOnUI() {
+    DCHECK_CURRENTLY_ON(BrowserThread::UI);
+    content::BrowserThread::PostTask(
+        content::BrowserThread::IO, FROM_HERE,
+        base::Bind(&PredictorBrowserTest::StartInterceptingHost,
+                   cross_site_test_server()->base_url()));
+  }
+
+  void StopInterceptingCrossSiteOnUI() {
+    DCHECK_CURRENTLY_ON(BrowserThread::UI);
+    content::BrowserThread::PostTask(
+        content::BrowserThread::IO, FROM_HERE,
+        base::Bind(&PredictorBrowserTest::StopInterceptingHost,
+                   cross_site_test_server()->base_url()));
   }
 
   void TearDownOnMainThread() override {
+    DCHECK_CURRENTLY_ON(BrowserThread::UI);
     ASSERT_TRUE(embedded_test_server()->ShutdownAndWaitUntilComplete());
   }
 
   // Navigates to a data URL containing the given content, with a MIME type of
   // text/html.
   void NavigateToDataURLWithContent(const std::string& content) {
+    DCHECK_CURRENTLY_ON(BrowserThread::UI);
     std::string encoded_content;
     base::Base64Encode(content, &encoded_content);
     std::string data_uri_content = "data:text/html;base64," + encoded_content;
@@ -254,29 +545,22 @@ 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 +583,511 @@ 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(const GURL& source_host,
+                                const GURL& cross_site_host) {
+    DCHECK_CURRENTLY_ON(BrowserThread::UI);
+    observer_.reset(
+        new CrossSitePredictorObserver(source_host, cross_site_host));
+    BrowserThread::PostTask(
+        BrowserThread::IO, FROM_HERE,
+        base::Bind(&PredictorBrowserTest::InstallPredictorObserverOnIOThread,
+                   base::Unretained(this), base::Unretained(predictor())));
+  }
+
+  void InstallPredictorObserverOnIOThread(
+      chrome_browser_net::Predictor* predictor) {
+    DCHECK_CURRENTLY_ON(BrowserThread::IO);
+    predictor->SetObserver(observer_.get());
+  }
+
+  // Note: For many of the tests to get to a "clean slate" mid run, they must
+  // flush sockets on both the client and server.
+  void FlushClientSockets() {
+    DCHECK_CURRENTLY_ON(BrowserThread::IO);
+    predictor()
+        ->url_request_context_getter_for_test()
+        ->GetURLRequestContext()
+        ->http_transaction_factory()
+        ->GetSession()
+        ->CloseAllConnections();
+  }
+
+  void FlushClientSocketsOnUIThread() {
+    DCHECK_CURRENTLY_ON(BrowserThread::UI);
+    base::RunLoop run_loop;
+    BrowserThread::PostTaskAndReply(
+        BrowserThread::IO, FROM_HERE,
+        base::Bind(&PredictorBrowserTest::FlushClientSockets,
+                   base::Unretained(this)),
+        run_loop.QuitClosure());
+    run_loop.Run();
+  }
+
+  void FlushServerSocketsOnUIThread(net::EmbeddedTestServer* test_server) {
+    DCHECK_CURRENTLY_ON(BrowserThread::UI);
+    EXPECT_TRUE(test_server->FlushAllSocketsAndConnectionsOnUIThread());
+  }
+
+  CrossSitePredictorObserver* observer() { return observer_.get(); }
+
+  // Navigate to an html file on embedded_test_server and tell it to request
+  // |num_cors| resources from the cross_site_test_server. It then waits for
+  // those requests to complete. Note that "cors" here means using cors-mode in
+  // correspondence with the fetch spec.
+  void NavigateToCrossSiteHtmlUrl(int num_cors, const char* file_suffix) {
+    DCHECK_CURRENTLY_ON(BrowserThread::UI);
+    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(),
+        "startFetchesAndWaitForReply()", &result));
+    EXPECT_TRUE(result);
+  }
+
   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_;
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
 };
 
-IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, PRE_ShutdownStartupCycle) {
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, SimplePreconnectOne) {
+  predictor()->PreconnectUrl(
+      embedded_test_server()->base_url(), GURL(),
+      UrlInfo::ResolutionMotivation::EARLY_LOAD_MOTIVATED,
+      false /* allow credentials */, 1);
+  connection_listener_->WaitForAcceptedConnectionsOnUI(1u);
+}
+
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, SimplePreconnectTwo) {
+  predictor()->PreconnectUrl(
+      embedded_test_server()->base_url(), GURL(),
+      UrlInfo::ResolutionMotivation::EARLY_LOAD_MOTIVATED,
+      false /* allow credentials */, 2);
+  connection_listener_->WaitForAcceptedConnectionsOnUI(2u);
+}
+
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, SimplePreconnectFour) {
+  predictor()->PreconnectUrl(
+      embedded_test_server()->base_url(), GURL(),
+      UrlInfo::ResolutionMotivation::EARLY_LOAD_MOTIVATED,
+      false /* allow credentials */, 4);
+  connection_listener_->WaitForAcceptedConnectionsOnUI(4u);
+}
+
+// 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) {
+  StopInterceptingCrossSiteOnUI();
+  NavigateToCrossSiteHtmlUrl(1 /* num_cors */, "" /* file_suffix */);
+  EXPECT_EQ(1u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(1, observer()->CrossSiteLearned());
+  EXPECT_EQ(2, observer()->SameSitePreconnected());
+}
+
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, CrossSiteUseThreeSockets) {
+  StopInterceptingCrossSiteOnUI();
+  NavigateToCrossSiteHtmlUrl(3 /* num_cors */, "" /* file_suffix */);
+  EXPECT_EQ(3u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(3, observer()->CrossSiteLearned());
+  EXPECT_EQ(2, observer()->SameSitePreconnected());
+}
+
+// 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.
+//
+// In order to simplify things, many of the following tests intercept requests
+// to the cross site test server. This allows the test server to maintain a
+// "clean slate" with no connected sockets, so that when the tests need to check
+// that predictor initiated preconnects occur, there are no races and the
+// connections are deterministic.
+//
+// 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 from the
+// predictor.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest,
+                       CrossSiteSimplePredictionAfterOneNavigation) {
+  NavigateToCrossSiteHtmlUrl(2 /* num_cors */, "" /* file_suffix */);
+  EXPECT_EQ(2, observer()->CrossSiteLearned());
+
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+
+  // Navigate again and confirm a preconnect. Note that because the two
+  // embedded test servers have the same host name, 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(4, observer()->CrossSitePreconnected());
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(4u);
+}
+
+// This test does not intercept initial requests / preconnects to the cross site
+// test server. This is a sanity check to make sure that the interceptor doesn't
+// change the logic in the predictor. Note that the test does not have the
+// ability to inspect at the socket layer, but verifies that the predictor is at
+// least making preconnect requests.
+IN_PROC_BROWSER_TEST_F(
+    PredictorBrowserTest,
+    CrossSiteSimplePredictionAfterOneNavigationNoInterceptor) {
+  StopInterceptingCrossSiteOnUI();
+  NavigateToCrossSiteHtmlUrl(1 /* num_cors */, "" /* file_suffix */);
+  EXPECT_EQ(1, observer()->CrossSiteLearned());
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(1u);
+
+  // 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"));
+  // Just check that predictor has initiated preconnects to the cross site test
+  // server. It's tricky to reset the connections to the test server, and
+  // sockets can be reused.
+  EXPECT_EQ(4, observer()->CrossSitePreconnected());
+}
+
+// Expect that the predictor correctly predicts subframe navigations.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, SubframeCrossSitePrediction) {
+  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(1, observer()->CrossSiteLearned());
+
+  // The subframe navigation initiates two preconnects.
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(2u);
+
+  FlushClientSocketsOnUIThread();
+  FlushServerSocketsOnUIThread(cross_site_test_server());
+  cross_site_connection_listener_->ResetCounts();
+
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+
+  // 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(4, observer()->CrossSitePreconnected());
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(4u);
+}
+
+// Expect that the predictor correctly preconnects an already learned resource
+// if the host shows up in a subframe. This test is equivalent to
+// CrossSiteSimplePredictionAfterOneNavigation, with the second navigation
+// (which initiates the preconnect) happening for a subframe load.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, SubframeInitiatesPreconnects) {
+  // Navigate to the normal cross site URL to learn the relationship.
+  NavigateToCrossSiteHtmlUrl(1 /* num_cors */, "" /* file_suffix */);
+  EXPECT_EQ(1, observer()->CrossSiteLearned());
+
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+
+  // 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(4, observer()->CrossSitePreconnected());
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(4u);
+}
+
+// Expect that the predictor correctly learns the subresources a subframe needs
+// to preconnect to.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest, SubframeLearning) {
+  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()));
+  EXPECT_EQ(1, observer()->CrossSiteLearned());
+
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+
+  // 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>");
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(4u);
+  EXPECT_EQ(4u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(4, observer()->CrossSitePreconnected());
+}
+
+// This test navigates to an html file with a tag:
+// <meta name="referrer" content="never">. This tests the implementation details
+// of the predictor. The current predictor only learns via the referrer header.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest,
+                       CrossSiteNoReferrerNoPredictionAfterOneNavigation) {
+  NavigateToCrossSiteHtmlUrl(2 /* num_cors */,
+                             "_no_referrer" /* file_suffix */);
+  EXPECT_EQ(0, observer()->CrossSiteLearned());
+  EXPECT_EQ(2, observer()->SameSitePreconnected());
+
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+
+  // Navigate again and confirm that no preconnects occurred.
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  EXPECT_EQ(0, observer()->CrossSitePreconnected());
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+}
+
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest,
+                       CrossSiteSimplePredictionAfterTwoNavigations) {
+  NavigateToCrossSiteHtmlUrl(1 /* num_cors */, "" /* file_suffix */);
+  EXPECT_EQ(0, observer()->CrossSitePreconnected());
+
+  NavigateToCrossSiteHtmlUrl(1 /* num_cors */, "" /* file_suffix */);
+  EXPECT_EQ(4, observer()->CrossSitePreconnected());
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(4u);
+
+  FlushClientSocketsOnUIThread();
+  FlushServerSocketsOnUIThread(cross_site_test_server());
+  cross_site_connection_listener_->ResetCounts();
+  observer()->ResetCounts();
+
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+
+  // 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) + .33)*.66) + 1 = 3 preconnects.
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  EXPECT_EQ(3, observer()->CrossSitePreconnected());
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(3u);
+}
+
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest,
+                       CrossSiteSimplePredictionAfterTwoNavigations2) {
+  NavigateToCrossSiteHtmlUrl(2 /* num_cors */, "" /* file_suffix */);
+  EXPECT_EQ(0, observer()->CrossSitePreconnected());
+
+  NavigateToCrossSiteHtmlUrl(2 /* num_cors */, "" /* file_suffix */);
+
+  EXPECT_EQ(4, observer()->CrossSitePreconnected());
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(4u);
+
+  FlushClientSocketsOnUIThread();
+  FlushServerSocketsOnUIThread(cross_site_test_server());
+  cross_site_connection_listener_->ResetCounts();
+  observer()->ResetCounts();
+
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+
+  // ((2 + .66) + .66)*.66 + 1 ~= 3.2.
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  EXPECT_EQ(4, observer()->CrossSitePreconnected());
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(4u);
+}
+
+// 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) {
+  NavigateToCrossSiteHtmlUrl(1 /* num_cors */, "" /* file_suffix */);
+  EXPECT_EQ(1, observer()->CrossSiteLearned());
+
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  // (2 + .33) + 1 = 3.33.
+  EXPECT_EQ(4, observer()->CrossSitePreconnected());
+  observer()->ResetCounts();
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  // ceil((2 + .33) * .66) + 1 = 3.
+  EXPECT_EQ(3, observer()->CrossSitePreconnected());
+  observer()->ResetCounts();
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  // ceil((2 + .33) * .66 * .66) + 1 = 3.
+  EXPECT_EQ(3, observer()->CrossSitePreconnected());
+  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(0, observer()->CrossSitePreconnected());
+}
+
+// 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) {
+  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(0, observer()->CrossSiteLearned());
+
+  EXPECT_EQ(2, observer()->CrossSitePreconnected());
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(2u);
+
+  FlushClientSocketsOnUIThread();
+  FlushServerSocketsOnUIThread(cross_site_test_server());
+  cross_site_connection_listener_->ResetCounts();
+  observer()->ResetCounts();
+
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+  EXPECT_EQ(0, observer()->CrossSitePreconnected());
+}
+
+// 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) {
+  ui_test_utils::NavigateToURL(browser(), embedded_test_server()->base_url());
+  EXPECT_EQ(1, observer()->CrossSiteLearned());
+
+  EXPECT_EQ(2, observer()->CrossSitePreconnected());
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(2u);
+
+  FlushClientSocketsOnUIThread();
+  FlushServerSocketsOnUIThread(cross_site_test_server());
+  cross_site_connection_listener_->ResetCounts();
+  observer()->ResetCounts();
+
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  // Preconnect 4 sockets because ceil(2 + .33) + 1 = 4.
+  EXPECT_EQ(4, observer()->CrossSitePreconnected());
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(4u);
+}
+
+// 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) {
+  std::string same_site_localhost_host = base::StringPrintf(
+      "%s://localhost:%s", embedded_test_server()->base_url().scheme().c_str(),
+      embedded_test_server()->base_url().port().c_str());
+  // The default predictor observer does not use "localhost".
+  InstallPredictorObserver(GURL(same_site_localhost_host),
+                           cross_site_test_server()->base_url());
+  GURL localhost_source = GURL(base::StringPrintf(
+      "%s/predictor/"
+      "predictor_cross_site.html?subresourceHost=%s&numCORSResources=1",
+      same_site_localhost_host.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(),
+      "startFetchesAndWaitForReply()", &result));
+  EXPECT_TRUE(result);
+
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+
+  ui_test_utils::NavigateToURL(
+      browser(), GURL(base::StringPrintf("%s/title1.html",
+                                         same_site_localhost_host.c_str())));
+  // Preconnect 3 sockets because ceil(2 + .33) = 3. Note that this time there
+  // is no additional connection due to same host.
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(3u);
+}
+
+// Perform the "/" redirect twice and make sure the predictor updates twice.
+IN_PROC_BROWSER_TEST_F(PredictorBrowserTest,
+                       CrossSiteTwoRedirectsPredictionWithNoPath) {
+  // Navigate once and redirect.
+  ui_test_utils::NavigateToURL(browser(), embedded_test_server()->base_url());
+  EXPECT_EQ(1, observer()->CrossSiteLearned());
+
+  EXPECT_EQ(2, observer()->CrossSitePreconnected());
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(2u);
+
+  FlushClientSocketsOnUIThread();
+  FlushServerSocketsOnUIThread(cross_site_test_server());
+  cross_site_connection_listener_->ResetCounts();
+  observer()->ResetCounts();
+
+  // Navigate again and redirect.
+  ui_test_utils::NavigateToURL(browser(), embedded_test_server()->base_url());
+  EXPECT_EQ(1, observer()->CrossSiteLearned());
+
+  // 2 + .33 + 1 = 3.33.
+  EXPECT_EQ(4, observer()->CrossSitePreconnected());
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(4u);
+
+  FlushClientSocketsOnUIThread();
+  FlushServerSocketsOnUIThread(cross_site_test_server());
+  cross_site_connection_listener_->ResetCounts();
+  observer()->ResetCounts();
+
+  EXPECT_EQ(0u, cross_site_connection_listener_->GetAcceptedSocketCount());
+
+  ui_test_utils::NavigateToURL(browser(),
+                               embedded_test_server()->GetURL("/title1.html"));
+  // 3 preconnects expected because ((2 + .33)*.66 + .33)*.66 + 1 = 2.23.
+  EXPECT_EQ(3, observer()->CrossSitePreconnected());
+  cross_site_connection_listener_->WaitForAcceptedConnectionsOnUI(3u);
+}
+
+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.
+  InstallPredictorObserver(referring_url_, target_url_);
   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;