Update perf page_set to use story_set

tools/perf/page_sets/service_worker_micro_benchmark.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 import story
 from telemetry.page import page as page
-from telemetry.page import page_set as page_set
-
 
 archive_data_file_path = 'data/service_worker_micro_benchmark.json'
 
 
 class ServiceWorkerBenchmarkPage(page.Page):
   """Page for workload to measure some specific functions in JS"""
 
   def RunNavigateSteps(self, action_runner):
     super(ServiceWorkerBenchmarkPage, self).RunNavigateSteps(action_runner)
     action_runner.WaitForJavaScriptCondition('window.done')
 
 
-class ServiceWorkerMicroBenchmarkPageSet(page_set.PageSet):
+class ServiceWorkerMicroBenchmarkPageSet(story.StorySet):
   """Page set for micro benchmarking of each functions with ServiceWorker"""
 
   def __init__(self):
     super(ServiceWorkerMicroBenchmarkPageSet, self).__init__(
         archive_data_file=archive_data_file_path,
-        bucket=page_set.PUBLIC_BUCKET)
+        cloud_storage_bucket=story.PUBLIC_BUCKET)
 
     # pylint: disable=C0301
     # The code of localhost:8091 is placed in
     # https://github.com/coonsta/Service-Worker-Performance
     # but currently the following is used:
     # https://github.com/amiq11/Service-Worker-Performance/tree/follow_spec_and_many_registration
     # (rev: 3238098ea0225f53dab2f69f7406db8a2712dbf9)
     # This will be merged into the main repository.
     # pylint: enable=C0301
     # Why: to measure performance of many concurrent fetches
     self.AddUserStory(ServiceWorkerBenchmarkPage(
         'http://localhost:8091/index.html', self,
         make_javascript_deterministic=False))