Update perf page_set to use story_set

tools/perf/page_sets/garbage_collection_cases.py

Index: tools/perf/page_sets/garbage_collection_cases.py
diff --git a/tools/perf/page_sets/garbage_collection_cases.py b/tools/perf/page_sets/garbage_collection_cases.py
index cf130a68ce7fe4835d91d3a5edf7be94bf35470b..5eaf5a35315d61f207e19ad2f38dee2cb9a23d00 100644
--- a/tools/perf/page_sets/garbage_collection_cases.py
+++ b/tools/perf/page_sets/garbage_collection_cases.py
@@ -2,8 +2,8 @@
 # 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):
@@ -27,7 +27,7 @@ class SpinningBallsPage(page_module.Page):
       action_runner.Wait(15)
 
 
-class GarbageCollectionCasesPageSet(page_set_module.PageSet):
+class GarbageCollectionCasesPageSet(story.StorySet):
 
   """
   Description: GC test cases
@@ -36,6 +36,6 @@ class GarbageCollectionCasesPageSet(page_set_module.PageSet):
   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))