Update perf page_set to use story_set

tools/perf/page_sets/key_silk_cases.py

Index: tools/perf/page_sets/key_silk_cases.py
diff --git a/tools/perf/page_sets/key_silk_cases.py b/tools/perf/page_sets/key_silk_cases.py
index 3eee569a8b425e9a156fc63d6a75418693145cc5..2800f140bc14f381c4ebbcf75cc8b06395b16eff 100644
--- a/tools/perf/page_sets/key_silk_cases.py
+++ b/tools/perf/page_sets/key_silk_cases.py
@@ -1,9 +1,9 @@
 # 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 shared_page_state
+from telemetry import story
 from telemetry.page import page as page_module
-from telemetry.page import page_set as page_set_module
+from telemetry.page import shared_page_state
 
 
 class KeySilkCasesPage(page_module.Page):
@@ -705,14 +705,14 @@ class Masonry(KeySilkCasesPage):
       action_runner.WaitForJavaScriptCondition('window.done')
 
 
-class KeySilkCasesPageSet(page_set_module.PageSet):
+class KeySilkCasesPageSet(story.StorySet):
 
   """ Pages hand-picked for project Silk. """
 
   def __init__(self, run_no_page_interactions=False):
     super(KeySilkCasesPageSet, self).__init__(
       archive_data_file='data/key_silk_cases.json',
-      bucket=page_set_module.PARTNER_BUCKET)
+      cloud_storage_bucket=story.PARTNER_BUCKET)
 
     self.AddUserStory(Page1(self, run_no_page_interactions))
     self.AddUserStory(Page2(self, run_no_page_interactions))