Introduce UserStory & UserStorySet classes.

tools/telemetry/telemetry/benchmark.py

Index: tools/telemetry/telemetry/benchmark.py
diff --git a/tools/telemetry/telemetry/benchmark.py b/tools/telemetry/telemetry/benchmark.py
index ec2c87534a526b12cf688d097cb2a1ffa1ce988f..88386cde413ce67262853b228b4f13bd16abe5df 100644
--- a/tools/telemetry/telemetry/benchmark.py
+++ b/tools/telemetry/telemetry/benchmark.py
@@ -84,15 +84,15 @@ class Benchmark(command_line.Command):
     if hasattr(self, '_enabled_strings'):
       pt._enabled_strings = self._enabled_strings
 
-    ps = self.CreatePageSet(finder_options)
     expectations = self.CreateExpectations()
+    us = self.CreateUserStorySet(finder_options)
 
     self._DownloadGeneratedProfileArchive(finder_options)
 
     benchmark_metadata = self.GetMetadata()
     results = results_options.CreateResults(benchmark_metadata, finder_options)
     try:
-      page_runner.Run(pt, ps, expectations, finder_options, results)
+      page_runner.Run(pt, us, expectations, finder_options, results)
     except page_test.TestNotSupportedOnPlatformFailure as failure:
       logging.warning(str(failure))
 
@@ -174,29 +174,23 @@ class Benchmark(command_line.Command):
       raise TypeError('"%s" is not a PageTest.' % cls.test.__name__)
     return cls.test
 
-  @classmethod
-  def PageSetClass(cls):
-    """Get the PageSet for this Benchmark.
+  def CreatePageSet(self, options):  # pylint: disable=W0613
+    """Get the page set this test will run on.
 
-    If the Benchmark has no PageSet, raises NotImplementedError.
+    By default, it will create a page set from the this test's page_set
+    attribute. Override to generate a custom page set.
     """
-    if not hasattr(cls, 'page_set'):
+    if not hasattr(self, 'page_set'):
       raise NotImplementedError('This test has no "page_set" attribute.')
-    if not issubclass(cls.page_set, page_set.PageSet):
-      raise TypeError('"%s" is not a PageSet.' % cls.page_set.__name__)
-    return cls.page_set
-
-  @classmethod
-  def CreatePageSet(cls, options):  # pylint: disable=W0613
-    """Get the page set this test will run on.
+    if not issubclass(self.page_set, page_set.PageSet):
+      raise TypeError('"%s" is not a PageSet.' % self.page_set.__name__)
+    return self.page_set()
 
-    By default, it will create a page set from the file at this test's
-    page_set attribute. Override to generate a custom page set.
-    """
-    return cls.PageSetClass()()
+  def CreateUserStorySet(self, options):
+    return self.CreatePageSet(options)
 
   @classmethod
-  def CreateExpectations(cls):  # pylint: disable=W0613
+  def CreateExpectations(cls):
     """Get the expectations this test will run with.
 
     By default, it will create an empty expectations set. Override to generate