Make credential_path a page attribute instead of page_set attribute.

tools/perf/page_sets/key_desktop_sites.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 KeyDesktopSitesPage(page_module.Page):
 
   def __init__(self, url, page_set):
-    super(KeyDesktopSitesPage, self).__init__(url=url, page_set=page_set)
-    self.credentials_path = 'data/credentials.json'
+    super(KeyDesktopSitesPage, self).__init__(
+        url=url, page_set=page_set, credentials_path = 'data/credentials.json')
     self.archive_data_file = 'data/key_desktop_sites.json'
 
   def RunSmoothness(self, action_runner):
     interaction = action_runner.BeginGestureInteraction(
         'ScrollAction', is_smooth=True)
     action_runner.ScrollPage()
     interaction.End()
 
 
 class FacebookPage(KeyDesktopSitesPage):
@@ skipping 89 matching lines @@
     action_runner.WaitForJavaScriptCondition(
         'document.getElementsByClassName("kix-appview-editor").length')
 
 
 class KeyDesktopSitesPageSet(page_set_module.PageSet):
 
   """ Sites of Interest """
 
   def __init__(self):
     super(KeyDesktopSitesPageSet, self).__init__(
-      credentials_path='data/credentials.json',
       archive_data_file='data/key_desktop_sites.json',
       bucket=page_set_module.PARTNER_BUCKET)
 
     self.AddPage(FacebookPage(self))
     self.AddPage(GmailPage(self))
     self.AddPage(GoogleCalendarPage(self))
     self.AddPage(GoogleDrivePage(self))
     self.AddPage(GoogleDocPage(self))
 
     urls_list = [
@@ skipping 712 matching lines @@
        '&q=black%20screen%20amd&colspec=ID%20Pri%20Mstone%20ReleaseBlock%20OS'
        '%20Area%20Feature%20Status%20Owner%20Summary'),
       'http://mlb.mlb.com/index.jsp',
       'http://www.nfl.com/',
       'http://airbnb.github.com/infinity/demo-on.html',
       'http://habrahabr.ru/post/149892/#habracut'
     ]
 
     for url in urls_list:
       self.AddPage(KeyDesktopSitesPage(url, self))