Introduce UserStory & UserStorySet classes.

tools/perf/benchmarks/benchmark_unittest.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.
 
 """Run the first page of every benchmark that has a composable measurement.
 
 Ideally this test would be comprehensive, but the above serves as a
 kind of smoke test.
 """
 
@@ skipping 19 matching lines @@
     # Only measure a single page so that this test cycles reasonably quickly.
     benchmark.options['pageset_repeat'] = 1
     benchmark.options['page_repeat'] = 1
 
     class SinglePageBenchmark(benchmark):  # pylint: disable=W0232
       def CreatePageSet(self, options):
         # pylint: disable=E1002
         ps = super(SinglePageBenchmark, self).CreatePageSet(options)
         for p in ps.pages:
           p.skip_waits = True
-          ps.pages = [p]
+          ps.user_stories = [p]
           break
         return ps
 
     # Set the benchmark's default arguments.
     options = options_for_unittests.GetCopy()
     options.output_format = 'none'
     options.suppress_gtest_report = True
     parser = options.CreateParser()
 
     benchmark.AddCommandLineArgs(parser)
@@ skipping 37 matching lines @@
     if hasattr(benchmark, 'generated_profile_archive'):
       # We'd like to test these, but don't know how yet.
       continue
 
     class BenchmarkSmokeTest(unittest.TestCase):
       pass
     setattr(BenchmarkSmokeTest, benchmark.Name(), SmokeTestGenerator(benchmark))
     suite.addTest(BenchmarkSmokeTest(benchmark.Name()))
 
   return suite