Make credential_path a page attribute instead of page_set attribute.

tools/perf/page_sets/top_desktop_sites_2012Q3.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_set
 from telemetry.page import page
 
 
 class Top2012Q3Page(page.Page):
 
   def __init__(self, url, ps):
-    super(Top2012Q3Page, self).__init__(url=url, page_set=ps)
+    super(Top2012Q3Page, self).__init__(
+        url=url, page_set=ps, credentials_path = 'data/credentials.json')
     self.make_javascript_deterministic = True
-    self.credentials_path = 'data/credentials.json'
     self.archive_data_file = 'data/2012Q3.json'
 
   def ReloadAndGc(self, action_runner):
     action_runner.ReloadPage()
     action_runner.Wait(1)
     action_runner.ForceGarbageCollection()
 
   def RunSmoothness(self, action_runner):
     interaction = action_runner.BeginGestureInteraction(
         'ScrollAction', is_smooth=True)
     action_runner.ScrollPage()
     interaction.End()
 
   def RunStressMemory(self, action_runner):
     for _ in xrange(3):
       self.ReloadAndGc(action_runner)
 
 
 class Top2012Q3PageSet(page_set.PageSet):
   """ Pages hand-picked from top-lists in Q32012. """
 
   def __init__(self):
     super(Top2012Q3PageSet, self).__init__(
       make_javascript_deterministic=True,
-      credentials_path='data/credentials.json',
       archive_data_file='data/2012Q3.json',
       bucket=page_set.PARTNER_BUCKET)
 
     urls_list = [
       'http://www.facebook.com/barackobama',
       'https://www.google.com/search?q=barack%20obama',
       'http://youtube.com',
       'http://yahoo.com',
       'http://www.baidu.com/s?wd=barack+obama',
       'http://en.wikipedia.org/wiki/Wikipedia',
@@ skipping 221 matching lines @@
       'http://www.target.com/c/women/-/N-5xtd3#?lnk=nav_t_spc_1_0',
       'http://dianxin.cn',
       'http://www.aizhan.com/siteall/www.youboy.com/',
       'http://veiculos-home.mercadolivre.com.br/',
       'http://kakaku.com',
       'http://flipkart.com',
       'http://paipai.com']
 
     for url in urls_list:
       self.AddPage(Top2012Q3Page(url, self))