Migrate from telemetry PageSet -> StorySet.

tools/chrome_proxy/integration_tests/chrome_proxy_pagesets/pass_through.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.page import page as page_module
-from telemetry.page import page_set as page_set_module
+from telemetry import story
 
 class PassThroughPage(page_module.Page):
   """
   A test page for the chrome proxy pass-through tests.
   """
 
   def __init__(self, url, page_set):
     super(PassThroughPage, self).__init__(url=url, page_set=page_set)
 
   def RunNavigateSteps(self, action_runner):
     super(PassThroughPage, self).RunNavigateSteps(action_runner)
     action_runner.ExecuteJavaScript('''
         (function() {
           var request = new XMLHttpRequest();
           request.open("GET", "%s");
           request.setRequestHeader("Chrome-Proxy", "pass-through");
           request.send(null);
         })();''' % (self.url))
     action_runner.Wait(1)
 
 
-class PassThroughPageSet(page_set_module.PageSet):
+class PassThroughStorySet(story.StorySet):
   """ Chrome proxy test sites """
 
   def __init__(self):
-    super(PassThroughPageSet, self).__init__()
+    super(PassThroughStorySet, self).__init__()
 
     urls_list = [
       'http://check.googlezip.net/image.png',
     ]
 
     for url in urls_list:
-      self.AddUserStory(PassThroughPage(url, self))
+      self.AddStory(PassThroughPage(url, self))