Make credential_path a page attribute instead of page_set attribute.

tools/perf/page_sets/calendar_forward_backward.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 CalendarForwardBackwardPage(page_module.Page):
 
   """ Why: Click forward(4x) and backwards(4x) repeatedly """
 
   def __init__(self, page_set):
     super(CalendarForwardBackwardPage, self).__init__(
       url='https://www.google.com/calendar/',
       page_set=page_set,
-      name='calendar_forward_backward')
-    self.credentials_path = 'data/credentials.json'
+      name='calendar_forward_backward',
+      credentials_path = 'data/credentials.json')
     self.credentials = 'google'
     self.user_agent_type = 'desktop'
     self.archive_data_file = 'data/calendar_forward_backward.json'
 
   def RunNavigateSteps(self, action_runner):
     action_runner.NavigateToPage(self)
     action_runner.Wait(2)
     action_runner.WaitForElement('div[class~="navForward"]')
     action_runner.ExecuteJavaScript('''
         (function() {
@@ skipping 29 matching lines @@
     action_runner.Wait(2)
     action_runner.WaitForElement('div[class~="navForward"]')
 
 
 class CalendarForwardBackwardPageSet(page_set_module.PageSet):
 
   """ Chrome Endure test for Google Calendar. """
 
   def __init__(self):
     super(CalendarForwardBackwardPageSet, self).__init__(
-      credentials_path='data/credentials.json',
       user_agent_type='desktop',
       archive_data_file='data/calendar_forward_backward.json',
       bucket=page_set_module.PUBLIC_BUCKET)
 
     self.AddPage(CalendarForwardBackwardPage(self))