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

BUG=90448
Review URL: https://chromiumcodereview.appspot.com/10829083

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@149002 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/renderer_host/render_view_host_manager_browsertest.cc

@@ -1013,6 +1013,11 @@ IN_PROC_BROWSER_TEST_F(RenderViewHostManagerTest, LeakingRenderViewHosts) {
 
   // 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());
 }