[Telemetry] Set youtube system health benchmarks to have platform specific recordings.

tools/perf/page_sets/system_health/browsing_stories.py

 # encoding: utf-8
 # 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 pinterest_login
 
@@ skipping 388 matching lines @@
 class YouTubeDesktopStory(_MediaBrowsingStory):
   NAME = 'browse:media:youtube'
   URL = 'https://www.youtube.com/watch?v=QGfhS1hfTWw&autoplay=false'
   ITEM_SELECTOR = '.yt-uix-simple-thumb-related'
   SUPPORTED_PLATFORMS = platforms.DESKTOP_ONLY
   IS_SINGLE_PAGE_APP = True
   # A longer view time allows videos to load and play.
   ITEM_VIEW_TIME_IN_SECONDS = 5
   ITEMS_TO_VISIT = 8
   ITEM_SELECTOR_INDEX = 3
+  PLATFORM_SPECIFIC = True
 
 
 class FacebookPhotosMobileStory(_MediaBrowsingStory):
   NAME = 'browse:media:facebook_photos'
   URL = (
       'https://m.facebook.com/rihanna/photos/a.207477806675.138795.10092511675/10153911739606676/?type=3&source=54&ref=page_internal')
   ITEM_SELECTOR = '._57-r.touchable'
   SUPPORTED_PLATFORMS = platforms.MOBILE_ONLY
   IS_SINGLE_PAGE_APP = True
   ITEM_SELECTOR_INDEX = 0
@@ skipping 53 matching lines @@
       inner_save_function = 'document.querySelector(".nameAndIcons")'
       action_runner.WaitForElement(element_function=inner_save_function)
       action_runner.ClickElement(element_function=inner_save_function)
       action_runner.Wait(1)  # Wait to make navigation realistic.
 
     # Close selection.
     x_element_function = ('document.querySelector('
                           '".Button.borderless.close.visible")')
     action_runner.ClickElement(element_function=x_element_function)
     action_runner.Wait(1)  # Wait to make navigation realistic.