Prerendered pages are swapped in at browser::Navigate time.

chrome/browser/prerender/prerender_browsertest.cc

 // Copyright (c) 2012 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 <deque>
 
 #include "base/command_line.h"
 #include "base/path_service.h"
 #include "base/stringprintf.h"
 #include "base/string_util.h"
@@ skipping 152 matching lines @@
     // TabContents, at the end of a navigation caused by a call to
     // NavigateToURLImpl().
     if (final_status() == FINAL_STATUS_USED)
       EXPECT_TRUE(new_render_view_host_);
 
     EXPECT_EQ(should_be_shown_, was_shown_);
 
     // When the PrerenderContents is destroyed, quit the UI message loop.
     // This happens on navigation to used prerendered pages, and soon
     // after cancellation of unused prerendered pages.
-    if (quit_message_loop_on_destruction_)
-      MessageLoopForUI::current()->Quit();
+    if (quit_message_loop_on_destruction_) {
+      // The message loop may not be running if this is swapped in
+      // synchronously on a Navigation.
+      MessageLoop* loop = MessageLoopForUI::current();
+      if (loop->is_running())
+        loop->Quit();
+    }
   }
 
   virtual void RenderViewGone(base::TerminationStatus status) OVERRIDE {
     // On quit, it's possible to end up here when render processes are closed
     // before the PrerenderManager is destroyed.  As a result, it's possible to
     // get either FINAL_STATUS_APP_TERMINATING or FINAL_STATUS_RENDERER_CRASHED
     // on quit.
     //
     // It's also possible for this to be called after we've been notified of
     // app termination, but before we've been deleted, which is why the second
@@ skipping 595 matching lines @@
           GetPrerenderContents()->prerender_contents()->web_contents();
       if (GetPrerenderContents()->number_of_loads() == 0) {
         page_load_observer.reset(
             new ui_test_utils::WindowedNotificationObserver(
                 content::NOTIFICATION_LOAD_STOP,
                 content::Source<NavigationController>(
                     &web_contents->GetController())));
       }
     }
 
-    // ui_test_utils::NavigateToURL waits until DidStopLoading is called on
-    // the current tab.  As that tab is going to end up deleted, and may never
-    // finish loading before that happens, exit the message loop on the deletion
-    // of the used prerender contents instead.
-    //
-    // As PrerenderTestURL waits until the prerendered page has completely
-    // loaded, there is no race between loading |dest_url| and swapping the
-    // prerendered TabContents into the tab.
+    // Navigate to the prerendered URL, but don't run the message loop. Browser
+    // issued navigations to prerendered pages will synchronously swap in the
+    // prerendered page.
     ui_test_utils::NavigateToURLWithDisposition(
         browser(), dest_url, disposition, ui_test_utils::BROWSER_TEST_NONE);
-    ui_test_utils::RunMessageLoop();
 
     // Make sure the PrerenderContents found earlier was used or removed.
     EXPECT_TRUE(GetPrerenderContents() == NULL);
 
     if (call_javascript_ && web_contents) {
       if (page_load_observer.get())
         page_load_observer->Wait();
 
       bool display_test_result = false;
       ASSERT_TRUE(ui_test_utils::ExecuteJavaScriptAndExtractBool(
@@ skipping 1135 matching lines @@
 IN_PROC_BROWSER_TEST_F(PrerenderBrowserTest, MatchCompleteDummy) {
   std::deque<FinalStatus> expected_final_status_queue;
   expected_final_status_queue.push_back(FINAL_STATUS_JAVASCRIPT_ALERT);
   expected_final_status_queue.push_back(FINAL_STATUS_WOULD_HAVE_BEEN_USED);
   PrerenderTestURL("files/prerender/prerender_alert_before_onload.html",
                    expected_final_status_queue, 1);
   NavigateToDestURL();
 }
 
 }  // namespace prerender