Make credential_path a page attribute instead of page_set attribute.

tools/perf/page_sets/top_10_mobile.py

 # Copyright 2014 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 telemetry.page import page as page_module
 from telemetry.page import page_set as page_set_module
 
 
 class Top10MobilePage(page_module.Page):
 
   def __init__(self, url, page_set):
-    super(Top10MobilePage, self).__init__(url=url, page_set=page_set)
-    self.credentials_path = 'data/credentials.json'
+    super(Top10MobilePage, self).__init__(
+        url=url, page_set=page_set, credentials_path = 'data/credentials.json')
     self.user_agent_type = 'mobile'
     self.archive_data_file = 'data/top_10_mobile.json'
 
   def RunSmoothness(self, action_runner):
     interaction = action_runner.BeginGestureInteraction(
         'ScrollAction', is_smooth=True)
     action_runner.ScrollPage()
     interaction.End()
 
 
 class Top10MobilePageSet(page_set_module.PageSet):
 
   """ Top 10 mobile sites """
 
   def __init__(self):
     super(Top10MobilePageSet, self).__init__(
-      credentials_path='data/credentials.json',
       user_agent_type='mobile',
       archive_data_file='data/top_10_mobile.json',
       bucket=page_set_module.PARTNER_BUCKET)
 
     urls_list = [
       # Why: #1 (Alexa) most visited page worldwide, picked a reasonable
       # search term
       'https://www.google.com/#hl=en&q=science',
       # Why: #2 (Alexa) most visited page worldwide, picked the most liked
       # page
@@ skipping 18 matching lines @@
       # Why: #13 (Alexa) most visited page worldwide, picked the first real
       # page
       'http://m.taobao.com/channel/act/mobile/20131111-women.html',
       # Why: #18 (Alexa) most visited page worldwide, picked a reasonable
       # search term
       'http://yandex.ru/touchsearch?text=science',
     ]
 
     for url in urls_list:
       self.AddPage(Top10MobilePage(url, self))