Make credential_path a page attribute instead of page_set attribute.

tools/perf/page_sets/mobile_memory.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 MobileMemoryPage(page_module.Page):
 
   def __init__(self, url, page_set):
-    super(MobileMemoryPage, self).__init__(url=url, page_set=page_set)
-    self.credentials_path = 'data/credentials.json'
+    super(MobileMemoryPage, self).__init__(
+        url=url, page_set=page_set, credentials_path = 'data/credentials.json')
     self.user_agent_type = 'mobile'
     self.archive_data_file = 'data/mobile_memory.json'
 
 
 class GmailPage(MobileMemoryPage):
 
   def __init__(self, page_set):
     super(GmailPage, self).__init__(
         url='https://mail.google.com/mail/mu',
         page_set=page_set)
@@ skipping 58 matching lines @@
     action_runner.ScrollPage()
     interaction.End()
 
 
 class MobileMemoryPageSet(page_set_module.PageSet):
 
   """ Mobile sites with interesting memory characteristics """
 
   def __init__(self):
     super(MobileMemoryPageSet, self).__init__(
-        credentials_path='data/credentials.json',
         user_agent_type='mobile',
         archive_data_file='data/mobile_memory.json',
         bucket=page_set_module.PARTNER_BUCKET)
 
     self.AddPage(GmailPage(self))
     self.AddPage(GoogleSearchPage(self))
 
     urls_list = [
       # Why: Renderer process memory bloat
       'http://techcrunch.com',
       # pylint: disable=C0301
       'http://techcrunch.com/2014/02/17/pixel-brings-brings-old-school-video-game-art-to-life-in-your-home/',
       'http://techcrunch.com/2014/02/15/kickstarter-coins-2/',
       'http://techcrunch.com/2014/02/15/was-y-combinator-worth-it/',
     ]
 
     for url in urls_list:
       self.AddPage(ScrollPage(url, self))