Update perf page_set to use story_set

tools/perf/page_sets/blob_workshop.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_test as page_test
-from telemetry.page import page_set as page_set_module
-
 
 NUM_BLOB_MASS_CREATE_READS = 15
 
 
 class BlobCreateThenRead(page_module.Page):
 
   def __init__(self, write_method, blob_sizes, page_set):
     super(BlobCreateThenRead, self).__init__(
       url='file://blob/blob-workshop.html',
       page_set=page_set,
@@ skipping 39 matching lines @@
                                            repeatable=True):
         action_runner.ExecuteJavaScript('readBlobsSerially();')
         action_runner.WaitForJavaScriptCondition(
             'doneReading === true || errors', 60)
 
     errors = action_runner.EvaluateJavaScript('errors')
     if errors:
       raise page_test.Failure('Errors on page: ' + ', '.join(self.errors))
 
 
-class BlobWorkshopPageSet(page_set_module.PageSet):
+class BlobWorkshopPageSet(story.StorySet):
   """The BlobWorkshop page set."""
 
   def __init__(self):
     super(BlobWorkshopPageSet, self).__init__()
     self.AddUserStory(
         BlobMassCreate('2Bx200', [2] * 200, self))
     self.AddUserStory(
         BlobMassCreate('1KBx200', [1024] * 200, self))
     self.AddUserStory(
         BlobMassCreate('150KBx200', [150 * 1024] * 200, self))
     self.AddUserStory(
         BlobMassCreate('1MBx200', [1024 * 1024] * 200, self))
     self.AddUserStory(
         BlobMassCreate('10MBx30', [10 * 1024 * 1024] * 30, self))
     self.AddUserStory(
         BlobMassCreate('100MBx5', [100 * 1024 * 1024] * 5, self))
 
     self.AddUserStory(BlobCreateThenRead('2Bx200', [2] * 200, self))
     self.AddUserStory(BlobCreateThenRead('1KBx200', [1024] * 200, self))
     self.AddUserStory(
         BlobCreateThenRead('150KBx200', [150 * 1024 - 1] * 200, self))
     self.AddUserStory(BlobCreateThenRead('1MBx200', [1024 * 1024] * 200, self))
     self.AddUserStory(
         BlobCreateThenRead('10MBx30', [10 * 1024 * 1024] * 30, self))
     self.AddUserStory(
         BlobCreateThenRead('100MBx5', [100 * 1024 * 1024] * 5, self))