[system health] Add desktop browsing story for facebook and change url of twitter story.

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 58 matching lines @@
 
 
 class LoadFacebookStory(_LoadingStory):
   # Using Facebook login often causes "404 Not Found" with WPR.
   NAME = 'load:social:facebook'
   URL = 'https://www.facebook.com/rihanna'
 
 
 class LoadTwitterStory(_LoadingStory):
   NAME = 'load:social:twitter'
-  URL = 'https://www.twitter.com/justinbieber?skip_interstitial=true'
+  URL = 'https://www.twitter.com/nasa'
 
 
 class LoadVkStory(_LoadingStory):
   NAME = 'load:social:vk'
   URL = 'https://vk.com/sbeatles'
   # Due to the deterministic date injected by WPR (February 2008), the cookie
   # set by https://vk.com immediately expires, so the page keeps refreshing
   # indefinitely on mobile
   # (see https://github.com/chromium/web-page-replay/issues/71).
   SUPPORTED_PLATFORMS = platforms.DESKTOP_ONLY
@@ skipping 267 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