Update perf page_set to use story_set

tools/perf/page_sets/tough_path_rendering_cases.py

 # Copyright 2015 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 import story
 from telemetry.page import page as page_module
-from telemetry.page import page_set as page_set_module
 
 
 class ToughPathRenderingCasesPage(page_module.Page):
 
   def RunPageInteractions(self, action_runner):
     with action_runner.CreateInteraction('ClickStart'):
       action_runner.Wait(10)
 
 
 class ChalkboardPage(page_module.Page):
 
   def RunPageInteractions(self, action_runner):
     with action_runner.CreateInteraction('ClickStart'):
       action_runner.EvaluateJavaScript(
           'document.getElementById("StartButton").click()')
       action_runner.Wait(20)
 
-class ToughPathRenderingCasesPageSet(page_set_module.PageSet):
+class ToughPathRenderingCasesPageSet(story.StorySet):
 
   """
   Description: Self-driven path rendering examples
   """
 
   def __init__(self):
     super(ToughPathRenderingCasesPageSet, self).__init__(
       archive_data_file='data/tough_path_rendering_cases.json',
-      bucket=page_set_module.PARTNER_BUCKET)
+      cloud_storage_bucket=story.PARTNER_BUCKET)
 
     urls_list = [
       'http://www.craftymind.com/factory/guimark2/HTML5ChartingTest.html'
     ]
 
     for url in urls_list:
       self.AddUserStory(ToughPathRenderingCasesPage(url, self))
 
     self.AddUserStory(ChalkboardPage(
         'http://ie.microsoft.com/testdrive/Performance/Chalkboard/', self))