Update reference to page_test module to use legacy_page_test module

tools/chrome_proxy/live_tests/chrome_proxy_measurements.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.
 
 import logging
 
 import chrome_proxy_metrics as metrics
 from common import chrome_proxy_measurements as measurements
 from telemetry.core import exceptions
-from telemetry.page import page_test
+from telemetry.page import legacy_page_test
 
-class ChromeProxyLatencyBase(page_test.PageTest):
+class ChromeProxyLatencyBase(legacy_page_test.LegacyPageTest):
   """Chrome latency measurement."""
 
   def __init__(self, *args, **kwargs):
     super(ChromeProxyLatencyBase, self).__init__(*args, **kwargs)
     self._metrics = metrics.ChromeProxyMetric()
 
   def WillNavigateToPage(self, page, tab):
     tab.ClearCache(force=True)
     self._metrics.Start(page, tab)
 
@@ skipping 19 matching lines @@
     options.AppendExtraBrowserArgs('--enable-spdy-proxy-auth')
 
 
 class ChromeProxyLatencyDirect(ChromeProxyLatencyBase):
   """Direct connection latency measurement."""
 
   def __init__(self, *args, **kwargs):
     super(ChromeProxyLatencyDirect, self).__init__(*args, **kwargs)
 
 
-class ChromeProxyDataSavingBase(page_test.PageTest):
+class ChromeProxyDataSavingBase(legacy_page_test.LegacyPageTest):
   """Chrome data saving measurement."""
   def __init__(self, *args, **kwargs):
     super(ChromeProxyDataSavingBase, self).__init__(*args, **kwargs)
     self._metrics = metrics.ChromeProxyMetric()
 
   def WillNavigateToPage(self, page, tab):
     tab.ClearCache(force=True)
     self._metrics.Start(page, tab)
 
   def ValidateAndMeasurePage(self, page, tab, results):
@@ skipping 15 matching lines @@
   def WillNavigateToPage(self, page, tab):
     measurements.WaitForViaHeader(tab)
     super(ChromeProxyDataSaving, self).WillNavigateToPage(page, tab)
 
 
 class ChromeProxyDataSavingDirect(ChromeProxyDataSavingBase):
   """Direct connection data saving measurement."""
 
   def __init__(self, *args, **kwargs):
     super(ChromeProxyDataSavingDirect, self).__init__(*args, **kwargs)