Revert of Change PageTest.WillStartBrowser to depend on platform instead of browser object as it would not ha…

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.
@@ skipping 20 matching lines @@
     self._power_metric = None
 
   def CustomizeBrowserOptions(self, options):
     options.AppendExtraBrowserArgs([
         '--enable-stats-collection-bindings'
     ])
     # Enable background networking so we can test its impact on power usage.
     options.disable_background_networking = False
     power.PowerMetric.CustomizeBrowserOptions(options)
 
-  def WillStartBrowser(self, platform):
+  def WillStartBrowser(self, browser):
     self._first_page_in_pageset = True
-    self._power_metric = power.PowerMetric(platform, TabSwitching.SAMPLE_TIME)
+    self._power_metric = power.PowerMetric(browser, TabSwitching.SAMPLE_TIME)
 
   def TabForPage(self, page, browser):
     if self._first_page_in_pageset:
       # The initial browser window contains a single tab, navigate that tab
       # rather than creating a new one.
       self._first_page_in_pageset = False
       return browser.tabs[0]
 
     return browser.tabs.New()
 
@@ skipping 38 matching lines @@
 
     last_histogram = histogram_util.GetHistogram(
         histogram_type, histogram_name, tab)
     diff_histogram = histogram_util.SubtractHistogram(last_histogram,
         first_histogram)
 
     results.AddSummaryValue(
         histogram.HistogramValue(None, display_name, '',
                                  raw_value_json=diff_histogram,
                                  important=False))