Add base::RunLoop and update ui_test_utils to use it to reduce flakiness

chrome/test/base/in_process_browser_test.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 "chrome/test/base/in_process_browser_test.h"
 
 #include "base/auto_reset.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/stack_trace.h"
@@ skipping 355 matching lines @@
   autorelease_pool_->Recycle();
 #endif
 
   // Invoke cleanup and quit even if there are failures. This is similar to
   // gtest in that it invokes TearDown even if Setup fails.
   CleanUpOnMainThread();
 #if defined(OS_MACOSX)
   autorelease_pool_->Recycle();
 #endif
 
+  // Sometimes tests leave Quit tasks in the MessageLoop (for shame), so let's
+  // run all pending messages here to avoid preempting the QuitBrowsers tasks.
+  // TODO(jbates) Once crbug.com/134753 is fixed, this can be removed because it
+  // will not be possible to post Quit tasks.
+  ui_test_utils::RunAllPendingInMessageLoop();
+
   QuitBrowsers();
   CHECK(BrowserList::empty());
 }
 
 void InProcessBrowserTest::QuitBrowsers() {
   if (BrowserList::empty())
     return;
 
   // Invoke AttemptExit on a running message loop.
   // AttemptExit exits the message loop after everything has been
@@ skipping 10 matching lines @@
   // On the Mac, this eventually reaches
   // -[BrowserWindowController windowWillClose:], which will post a deferred
   // -autorelease on itself to ultimately destroy the Browser object. The line
   // below is necessary to pump these pending messages to ensure all Browsers
   // get deleted.
   ui_test_utils::RunAllPendingInMessageLoop();
   delete autorelease_pool_;
   autorelease_pool_ = NULL;
 #endif
 }