[system-health] Add support for disabling individual stories on individual platforms

tools/perf/page_sets/system_health/searching_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 telemetry import decorators
 
+
+@decorators.Disabled('win')  # http://crbug.com/642463
 class SearchGoogleStory(system_health_story.SystemHealthStory):
   NAME = 'search:portal:google'
   URL = 'https://www.google.co.uk/'
-  # Tap simulation doesn't fully work on Windows. http://crbug.com/634343
-  SUPPORTED_PLATFORMS = platforms.MOBILE_ONLY
 
   _SEARCH_BOX_SELECTOR = 'input[aria-label="Search"]'
   _RESULT_SELECTOR = '.r > a[href*="wikipedia"]'
 
   def _DidLoadDocument(self, action_runner):
     # Click on the search box.
     action_runner.Wait(1)
     action_runner.WaitForElement(selector=self._SEARCH_BOX_SELECTOR)
     action_runner.TapElement(selector=self._SEARCH_BOX_SELECTOR)
 
@@ skipping 15 matching lines @@
         })()''' % self._RESULT_SELECTOR)
     while action_runner.EvaluateJavaScript(result_visible_expression):
       action_runner.RepeatableBrowserDrivenScroll(y_scroll_distance_ratio=0.75,
                                                   prevent_fling=False)
       action_runner.Wait(0.2)
 
     # Click on the Wikipedia result.
     action_runner.Wait(1)
     action_runner.TapElement(selector=self._RESULT_SELECTOR)
     action_runner.tab.WaitForDocumentReadyStateToBeComplete()