Migrate from telemetry PageSet -> StorySet.

tools/chrome_proxy/integration_tests/chrome_proxy_pagesets/block_once.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.page import page as page_module
-from telemetry.page import page_set as page_set_module
+from telemetry import story
 
 
 class BlockOncePage(page_module.Page):
 
   def __init__(self, url, page_set):
     super(BlockOncePage, self).__init__(url=url, page_set=page_set)
 
   def RunNavigateSteps(self, action_runner):
     super(BlockOncePage, self).RunNavigateSteps(action_runner)
     # Test block-once on a POST request.
     # Ensure that a subsequent request uses the data reduction proxy.
     action_runner.ExecuteJavaScript('''
       (function() {
         var request = new XMLHttpRequest();
         request.open("POST",
             "http://chromeproxy-test.appspot.com/default?respBody=T0s=&respStatus=200&flywheelAction=block-once");
         request.onload = function() {
           var viaProxyRequest = new XMLHttpRequest();
           viaProxyRequest.open("GET",
               "http://check.googlezip.net/image.png");
           viaProxyRequest.send();
         };
         request.send();
       })();
     ''')
     action_runner.Wait(1)
 
-class BlockOncePageSet(page_set_module.PageSet):
+class BlockOnceStorySet(story.StorySet):
 
   """ Chrome proxy test sites """
 
   def __init__(self):
-    super(BlockOncePageSet, self).__init__()
+    super(BlockOnceStorySet, self).__init__()
 
     # Test block-once for a GET request.
     urls_list = [
       'http://check.googlezip.net/blocksingle/',
     ]
 
     for url in urls_list:
-      self.AddUserStory(BlockOncePage(url, self))
+      self.AddStory(BlockOncePage(url, self))