[system health] Add flipboard to system health stories.

tools/perf/page_sets/system_health/loading_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 system_health_story
 
 from page_sets.login_helpers import dropbox_login
 from page_sets.login_helpers import google_login
 
@@ skipping 104 matching lines @@
   # Redirects to the "http://" version.
   URL = 'https://www.bbc.co.uk/news/world-asia-china-36189636'
 
 
 class LoadCnnStory(_LoadingStory):
   NAME = 'load:news:cnn'
   # Using "https://" shows "Your connection is not private".
   URL = 'http://edition.cnn.com'
 
 
+class LoadFacebookStory(_LoadingStory):
+  NAME = 'load:news:flipboard'
+  URL = 'https://flipboard.com/explore'
+
+
 class LoadHackerNewsStory(_LoadingStory):
   NAME = 'load:news:hackernews'
   URL = 'https://news.ycombinator.com'
 
 
 class LoadNytimesDesktopStory(_LoadingStory):
   NAME = 'load:news:nytimes'
   URL = 'http://www.nytimes.com'
   SUPPORTED_PLATFORMS = platforms.DESKTOP_ONLY
 
@@ skipping 222 matching lines @@
   URL = 'http://www.miniclip.com/games/en/'
   # Desktop only (requires Flash).
   SUPPORTED_PLATFORMS = platforms.DESKTOP_ONLY
 
 
 class LoadAlphabettyStory(_LoadingStory):
   NAME = 'load:games:alphabetty'
   URL = 'https://king.com/play/alphabetty'
   # Desktop only (requires Flash).
   SUPPORTED_PLATFORMS = platforms.DESKTOP_ONLY