Make credential_path a page attribute instead of page_set attribute.

tools/perf/page_sets/key_search_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 KeySearchMobilePage(page_module.Page):
 
   def __init__(self, url, page_set):
-    super(KeySearchMobilePage, self).__init__(url=url, page_set=page_set)
-    self.credentials_path = 'data/credentials.json'
+    super(KeySearchMobilePage, self).__init__(
+        url=url, page_set=page_set, credentials_path = 'data/credentials.json')
     self.user_agent_type = 'mobile'
     self.archive_data_file = 'data/key_search_mobile.json'
 
   def RunSmoothness(self, action_runner):
     interaction = action_runner.BeginGestureInteraction(
         'ScrollAction', is_smooth=True)
     action_runner.ScrollPage()
     interaction.End()
 
 
 class KeySearchMobilePageSet(page_set_module.PageSet):
 
   """ Key mobile search queries on google """
 
   def __init__(self):
     super(KeySearchMobilePageSet, self).__init__(
-      credentials_path='data/credentials.json',
       user_agent_type='mobile',
       archive_data_file='data/key_search_mobile.json',
       bucket=page_set_module.PUBLIC_BUCKET)
 
     urls_list = [
       # Why: An empty page should be as snappy as possible
       'http://www.google.com/',
       # Why: A reasonable search term with no images or ads usually
       'https://www.google.com/search?q=science',
       # Why: A reasonable search term with images but no ads usually
@@ skipping 20 matching lines @@
       # Why: Definitions
       'http://www.google.com/search?q=define+define',
       # Why: Local results
       'https://www.google.com/search?q=burritos+94110',
       # Why: Graph
       'http://www.google.com/search?q=x^3'
     ]
 
     for url in urls_list:
       self.AddPage(KeySearchMobilePage(url, self))