Fix RenderViewHostManagerTest.LeakingRenderViewHosts on cros by flushing the message loop.

content/browser/renderer_host/render_view_host_manager_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 "base/file_util.h"
 #include "base/memory/ref_counted.h"
 #include "base/path_service.h"
 #include "base/utf_string_conversions.h"
 #include "content/browser/renderer_host/render_view_host_impl.h"
 #include "content/browser/site_instance_impl.h"
@@ skipping 995 matching lines @@
 
   // Ensure that view-source navigations force a new SiteInstance.
   EXPECT_NE(site_instance1, site_instance2);
 
   // Now navigate to a different instance so that we swap out again.
   NavigateToURL(shell(), https_server.GetURL("files/title2.html"));
   rvh_observers.AddObserverToRVH(shell()->web_contents()->GetRenderViewHost());
 
   // This used to leak a render view host.
   shell()->Close();
+
+  MessageLoop::current()->PostTask(FROM_HERE,
+                                   MessageLoop::QuitWhenIdleClosure());
+  content::RunMessageLoop();
+
   EXPECT_EQ(0U, rvh_observers.GetNumObservers());
 }
 
 }  // namespace content