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

chrome/test/perf/rendering/throughput_tests.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/command_line.h"
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/json/json_reader.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/path_service.h"
@@ skipping 179 matching lines @@
     } else {
       command_line->AppendSwitch(switches::kDisableAcceleratedCompositing);
       command_line->AppendSwitch(switches::kDisableExperimentalWebGL);
       command_line->AppendSwitch(switches::kDisableAccelerated2dCanvas);
     }
   }
 
   void Wait(int ms) {
     MessageLoop::current()->PostDelayedTask(
         FROM_HERE,
-        MessageLoop::QuitClosure(),
+        MessageLoop::QuitNowClosure(),
         base::TimeDelta::FromMilliseconds(ms));
     ui_test_utils::RunMessageLoop();
   }
 
   // Take snapshot of the current tab, encode it as PNG, and save to a SkBitmap.
   bool TabSnapShotToImage(SkBitmap* bitmap) {
     CHECK(bitmap);
     std::vector<unsigned char> png;
 
     gfx::Rect root_bounds = browser()->window()->GetBounds();
@@ skipping 347 matching lines @@
 
 IN_PROC_BROWSER_TEST_F(ThroughputTestSW, CanvasManyImagesSW) {
   RunCanvasBenchTest("many_images", kNone);
 }
 
 IN_PROC_BROWSER_TEST_F(ThroughputTestGPU, CanvasManyImagesGPU) {
   RunCanvasBenchTest("many_images", kNone | kIsGpuCanvasTest);
 }
 
 }  // namespace