Update reference to page_test module to use legacy_page_test module

chrome/test/media_router/telemetry/benchmarks/media_router_measurements.py

 # Copyright 2016 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 benchmarks import media_router_dialog_metric
 from benchmarks import media_router_cpu_memory_metric
-from telemetry.page import page_test
+from telemetry.page import legacy_page_test
 
 
-class MediaRouterDialogTest(page_test.PageTest):
+class MediaRouterDialogTest(legacy_page_test.LegacyPageTest):
   """Performs a measurement of Media Route dialog latency."""
 
   def __init__(self):
     super(MediaRouterDialogTest, self).__init__()
     self._metric = media_router_dialog_metric.MediaRouterDialogMetric()
 
   def DidNavigateToPage(self, page, tab):
     self._metric.Start(page, tab)
 
   def ValidateAndMeasurePage(self, page, tab, results):
     self._metric.Stop(page, tab)
     self._metric.AddResults(tab, results)
 
 
-class MediaRouterCPUMemoryTest(page_test.PageTest):
+class MediaRouterCPUMemoryTest(legacy_page_test.LegacyPageTest):
   """Performs a measurement of Media Route CPU/memory usage."""
 
   def __init__(self):
     super(MediaRouterCPUMemoryTest, self).__init__()
     self._metric = media_router_cpu_memory_metric.MediaRouterCPUMemoryMetric()
 
   def ValidateAndMeasurePage(self, page, tab, results):
     self._metric.AddResults(tab, results)