Update reference to page_test module to use legacy_page_test module

tools/chrome_proxy/common/network_metrics.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.
 
 import base64
 import gzip
 import hashlib
 import io
 import logging
 import os
 import sys
 import zlib
 
 from common import inspector_network
 from telemetry.timeline import model
 
 sys.path.append(
     os.path.join(os.path.dirname(__file__), os.pardir, os.pardir, 'perf'))
 from metrics import Metric
 
-from telemetry.page import page_test
+from telemetry.page import legacy_page_test
 # All network metrics are Chrome only for now.
 from telemetry.value import scalar
 
 
 class NetworkMetricException(page_test.MeasurementFailure):
   pass
 
 
 class HTTPResponse(object):
   """ Represents an HTTP response from a timeline event."""
@@ skipping 178 matching lines @@
     if self.compute_data_saving:
       if (original_content_length > 0 and
           original_content_length >= content_length):
         saving = (float(original_content_length-content_length) * 100 /
                   original_content_length)
         results.AddValue(scalar.ScalarValue(
             results.current_page, 'data_saving', 'percent', saving))
       else:
         results.AddValue(scalar.ScalarValue(
             results.current_page, 'data_saving', 'percent', 0.0))