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

chrome/browser/prerender/prerender_browsertest.cc

Index: chrome/browser/prerender/prerender_browsertest.cc
diff --git a/chrome/browser/prerender/prerender_browsertest.cc b/chrome/browser/prerender/prerender_browsertest.cc
index c98d0bfe929fbb4f0ed7695350b44021af56d8a2..f1ab3949a7ecb7fa49de0a608db7eacb7d5dba03 100644
--- a/chrome/browser/prerender/prerender_browsertest.cc
+++ b/chrome/browser/prerender/prerender_browsertest.cc
@@ -170,8 +170,13 @@ class TestPrerenderContents : public PrerenderContents {
     // 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 {
@@ -786,17 +791,11 @@ class PrerenderBrowserTest : public InProcessBrowserTest {
       }
     }
 
-    // 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);