[tools/perf] Reference legacy_page_test module instead of page_test

tools/perf/measurements/tab_switching.py

 # Copyright 2013 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.
 
 """The tab switching measurement.
 
 This measurement opens pages in different tabs. After all the tabs have opened,
 it cycles through each tab in sequence, and records a histogram of the time
 between when a tab was first requested to be shown, and when it was painted.
 Power usage is also measured.
 """
 
 import time
 
 from telemetry.core import util
-from telemetry.page import page_test
+from telemetry.page import legacy_page_test
 from telemetry.value import histogram
 from telemetry.value import histogram_util
 
 from metrics import keychain_metric
 from metrics import power
 
 # TODO: Revisit this test once multitab support is finalized.
 
 
-class TabSwitching(page_test.PageTest):
+class TabSwitching(legacy_page_test.LegacyPageTest):
 
   # Amount of time to measure, in seconds.
   SAMPLE_TIME = 30
 
   def __init__(self):
     super(TabSwitching, self).__init__()
     self.first_page_in_storyset = True
     self._power_metric = None
 
   def CustomizeBrowserOptions(self, options):
@@ skipping 65 matching lines @@
 
     results.AddSummaryValue(
         histogram.HistogramValue(None, display_name, 'ms',
                                  raw_value_json=diff_histogram,
                                  important=False))
 
     keychain_metric.KeychainMetric().AddResults(tab, results)
 
   def DidRunPage(self, platform):
     self._power_metric.Close()