Update perf page_set to use story_set

tools/perf/page_sets/garbage_collection_cases.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.
 # pylint: disable=W0401,W0614
+from telemetry import story
 from telemetry.page import page as page_module
-from telemetry.page import page_set as page_set_module
 
 
 class SpinningBallsPage(page_module.Page):
 
   def __init__(self, page_set):
     super(SpinningBallsPage, self).__init__(
       # pylint: disable=C0301
       url='http://v8.googlecode.com/svn/branches/bleeding_edge/benchmarks/spinning-balls/index.html',
       page_set=page_set)
 
   def RunNavigateSteps(self, action_runner):
     super(SpinningBallsPage, self).RunNavigateSteps(action_runner)
     action_runner.WaitForJavaScriptCondition(
         "document.readyState == 'complete'")
     action_runner.ClickElement(selector='input[type="submit"]')
     action_runner.WaitForJavaScriptCondition(
         "document.readyState == 'complete'")
 
   def RunPageInteractions(self, action_runner):
     with action_runner.CreateInteraction('RunSmoothAllActions'):
       action_runner.Wait(15)
 
 
-class GarbageCollectionCasesPageSet(page_set_module.PageSet):
+class GarbageCollectionCasesPageSet(story.StorySet):
 
   """
   Description: GC test cases
   """
 
   def __init__(self):
     super(GarbageCollectionCasesPageSet, self).__init__(
       archive_data_file='data/garbage_collection_cases.json',
-      bucket=page_set_module.PARTNER_BUCKET)
+      cloud_storage_bucket=story.PARTNER_BUCKET)
 
     self.AddUserStory(SpinningBallsPage(self))