[system health] Re-enable about:blank and browse:news:cnn on win

tools/perf/page_sets/system_health/blank_stories.py

 # Copyright 2016 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.
 
 from page_sets.system_health import system_health_story
 
-from telemetry import decorators
 
-@decorators.Disabled('win') # crbug.com/656040
 class BlankAboutBlankStory(system_health_story.SystemHealthStory):
   """Story that loads the about:blank page."""
 
   NAME = 'blank:about:blank'
   URL = 'about:blank'
 
   def _DidLoadDocument(self, action_runner):
     # Request a RAF and wait for it to be processed to ensure that the metric
     # Startup.FirstWebContents.NonEmptyPaint2 is recorded.
     action_runner.ExecuteJavaScript(
         """
         window.__hasRunRAF = false;
         requestAnimationFrame(function() {
           window.__hasRunRAF = true;
         });
         """
     )
     action_runner.WaitForJavaScriptCondition("window.__hasRunRAF")