Update perf page_set to use story_set

tools/perf/page_sets/blob_workshop.py

Index: tools/perf/page_sets/blob_workshop.py
diff --git a/tools/perf/page_sets/blob_workshop.py b/tools/perf/page_sets/blob_workshop.py
index ff8715f6e7c8bf3156c1c677ba561d824f10dcb4..81d50f3e7357049099d7631476c97d549a84f8f5 100644
--- a/tools/perf/page_sets/blob_workshop.py
+++ b/tools/perf/page_sets/blob_workshop.py
@@ -2,10 +2,9 @@
 # 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
 
@@ -65,7 +64,7 @@ class BlobMassCreate(page_module.Page):
       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):