[system health] Make mobile washington post story more robust.

tools/perf/page_sets/system_health/browsing_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
 
 
 class _BrowsingStory(system_health_story.SystemHealthStory):
   """Abstract base class for browsing stories.
@@ skipping 180 matching lines @@
 
 
 class WashingtonPostMobileStory(_NewsBrowsingStory):
   """Progressive website"""
   NAME = 'browse:news:washingtonpost'
   URL = 'https://www.washingtonpost.com/pwa'
   IS_SINGLE_PAGE_APP = True
   ITEM_SELECTOR = '.hed > a'
   SUPPORTED_PLATFORMS = platforms.MOBILE_ONLY
   _CLOSE_BUTTON_SELECTOR = '.close'
+  _MAIL_BUTTON_SELECTOR = '.mailBlock'
 
   def _DidLoadDocument(self, action_runner):
     # Close the popup window. On Nexus 9 (and probably other tables) the popup
     # window does not have a "Close" button, instead it has only a "Send link
     # to phone" button. So on tablets we run with the popup window open. The
     # popup is transparent, so this is mostly an aesthetical issue.
-    has_button = action_runner.EvaluateJavaScript(
+    action_runner.WaitForElement(selector="%s, %s" %
+        (self._CLOSE_BUTTON_SELECTOR, self._MAIL_BUTTON_SELECTOR))
+    has_close_button = action_runner.EvaluateJavaScript(
         '!!document.querySelector("%s")' % self._CLOSE_BUTTON_SELECTOR)
-    if has_button:
+    if has_close_button:
       action_runner.ClickElement(selector=self._CLOSE_BUTTON_SELECTOR)
     super(WashingtonPostMobileStory, self)._DidLoadDocument(action_runner)