Fix cases where RunLoop is created without a MessageLoop.

chrome/browser/chromeos/login/screenshot_testing/screenshot_tester.cc

 // Copyright 2014 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/browser/chromeos/login/screenshot_testing/screenshot_tester.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "ash/shell.h"
 #include "base/command_line.h"
 #include "base/files/file_util.h"
+#include "base/run_loop.h"
 #include "chrome/browser/chromeos/login/screenshot_testing/SkDiffPixelsMetric.h"
 #include "chrome/browser/chromeos/login/screenshot_testing/SkImageDiffer.h"
 #include "chrome/browser/chromeos/login/screenshot_testing/SkPMetric.h"
 #include "chromeos/chromeos_switches.h"
 #include "content/public/browser/browser_thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "ui/compositor/compositor_switches.h"
 #include "ui/gfx/codec/png_codec.h"
 #include "ui/gfx/image/image.h"
@@ skipping 325 matching lines @@
 
   ScreenshotTester::Result testing_result;
   testing_result.similarity = result.result;
   testing_result.screenshots_match =
       (result.result == SkImageDiffer::RESULT_CORRECT);
 
   return testing_result;
 }
 
 }  // namespace chromeos