[tools/perf] Reference legacy_page_test module instead of page_test

tools/perf/benchmarks/dummy_benchmark.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.
 """Dummy benchmarks for the bisect FYI integration tests.
 
 The number they produce aren't meant to represent any actual performance
 data of the browser. For more information about these dummy benchmarks,
 see: https://goo.gl/WvZiiW
 """
 
 import random
 
 from core import perf_benchmark
 
 from telemetry.value import scalar
-from telemetry.page import page_test
+from telemetry.page import legacy_page_test
 
 from page_sets import dummy_story_set
 
 
-class _DummyTest(page_test.PageTest):
+class _DummyTest(legacy_page_test.LegacyPageTest):
 
   def __init__(self, avg, std):
     super(_DummyTest, self).__init__()
     self._avg = avg
     self._std = std
 
   def ValidateAndMeasurePage(self, page, tab, results):
     results.AddValue(scalar.ScalarValue(
         page=page,
         name='gaussian-value', units='ms',
@@ skipping 19 matching lines @@
 
 class DummyBenchmarkTwo(_DummyBenchmark):
   """A noisy benchmark with mean=50 & std=20."""
 
   def CreatePageTest(self, options):
     return _DummyTest(50, 20)
 
   @classmethod
   def Name(cls):
     return 'dummy_benchmark.noisy_benchmark_1'