Make credential_path a page attribute instead of page_set attribute.

tools/perf/page_sets/top_10.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 SimpleScrollPage(page_module.Page):
   def __init__(self, url, page_set, credentials='', name=''):
-    super(SimpleScrollPage, self).__init__(url, page_set=page_set, name=name)
+    super(SimpleScrollPage, self).__init__(
+        url, page_set=page_set, name=name,
+        credentials_path='data/credentials.json')
     self.credentials = credentials
 
   def RunSmoothness(self, action_runner):
     interaction = action_runner.BeginGestureInteraction(
         'ScrollAction', is_smooth=True)
     action_runner.ScrollPage()
     interaction.End()
 
 class Google(SimpleScrollPage):
   def __init__(self, page_set):
@@ skipping 62 matching lines @@
     super(Facebook, self).RunNavigateSteps(action_runner)
     action_runner.WaitForElement(text='About')
 
 
 class Top10PageSet(page_set_module.PageSet):
   """10 Pages chosen from Alexa top sites"""
 
   def __init__(self):
     super(Top10PageSet, self).__init__(
       archive_data_file='data/top_10.json',
-      credentials_path='data/credentials.json',
       user_agent_type='desktop',
       bucket=page_set_module.PARTNER_BUCKET)
 
     # top google property; a google tab is often open
     self.AddPage(Google(self))
 
     # productivity, top google properties
     # TODO(dominikg): fix crbug.com/386152
     #self.AddPage(Gmail(self))
 
@@ skipping 14 matching lines @@
     self.AddPage(SimpleScrollPage('http://www.amazon.com', self))
 
     # #4 Alexa
     self.AddPage(SimpleScrollPage('http://www.yahoo.com/', self))
 
     # #16 Alexa
     self.AddPage(SimpleScrollPage('http://www.bing.com/', self))
 
     # #20 Alexa
     self.AddPage(SimpleScrollPage('http://www.ask.com/', self))