Add Javascript-Heavy tags for system health stories with heavy uses of JS

tools/perf/page_sets/system_health/background_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 platforms
+from page_sets.system_health import story_tags
 from page_sets.system_health import system_health_story
 from page_sets.system_health.loading_stories import LoadGmailMobileStory
 
 from telemetry import decorators
 
 _WAIT_FOR_VIDEO_SECONDS = 5
 
 class _BackgroundStory(system_health_story.SystemHealthStory):
   """Abstract base class for background stories
 
@@ skipping 23 matching lines @@
   NAME = 'background:social:facebook'
   URL = 'https://www.facebook.com/rihanna'
   SUPPORTED_PLATFORMS = platforms.MOBILE_ONLY
 
 
 class BackgroundNytimesMobileStory(_BackgroundStory):
   """The third top website in http://www.alexa.com/topsites/category/News"""
   NAME = 'background:news:nytimes'
   URL = 'http://www.nytimes.com/2016/10/04/us/politics/vice-presidential-debate.html?_r=0'
   SUPPORTED_PLATFORMS = platforms.MOBILE_ONLY
+  TAGS = [story_tags.JAVASCRIPT_HEAVY]
 
   def _DidLoadDocument(self, action_runner):
     # Dismiss the 'You have n free articles' message.
     action_runner.WaitForElement(selector='.growl-dismiss')
     action_runner.TapElement(selector='.growl-dismiss')
 
     # Tap the 'Show Full Article' button.
     action_runner.WaitForElement(selector='#additional-content button')
     action_runner.ScrollPageToElement(selector='#additional-content button')
     # TapElement seems flaky here so use JavaScript instead.
@@ skipping 20 matching lines @@
 
 
 @decorators.Disabled('android')  # crbug.com/676336
 class BackgroundGmailMobileStory(LoadGmailMobileStory):
   NAME = 'background:tools:gmail'
   SUPPORTED_PLATFORMS = platforms.MOBILE_ONLY
 
   def _Measure(self, action_runner):
     action_runner.tab.browser.Background()
     super(BackgroundGmailMobileStory, self)._Measure(action_runner)