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.

[dominich, 2012/02/28 16:21:00]

Is it worth splitting the tests into browser- and render-initiated tests? it
might simplify the message loop handling with your new change as we could test
the majority of the code under the browser and then test some core functionality
under render.

+      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 594 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 1130 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