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.
+      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);