[Telemetry] Measure power in tab_switching measurement

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 metrics import cpu
 from metrics import histogram_util
+from metrics import power
 from telemetry.core import util
 from telemetry.page import page_measurement
 
 # TODO: Revisit this test once multitab support is finalized.
 
 class TabSwitching(page_measurement.PageMeasurement):
   def __init__(self):
     super(TabSwitching, self).__init__()
-    self._cpu_metric = None
+    self._first_page_in_pageset = True
+    self._power_metric = power.PowerMetric()
 
   def CustomizeBrowserOptions(self, options):
     options.AppendExtraBrowserArgs([
         '--enable-stats-collection-bindings'
     ])
+    power.PowerMetric.CustomizeBrowserOptions(options)
+
+  def DidStartBrowser(self, browser):
+    self._first_page_in_pageset = True
 
   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()
 
-  def DidStartBrowser(self, browser):
-    self._cpu_metric = cpu.CpuMetric(browser)
+  def StopBrowserAfterPage(self, browser, page):
+    # Restart the browser after the last page in the pageset.
+    return len(browser.tabs) >= len(page.page_set.pages)
 
   def MeasurePage(self, page, tab, results):
     """On the last tab, cycle through each tab that was opened and then record
     a single histogram for the tab switching metric."""
     if len(tab.browser.tabs) != len(page.page_set.pages):
       return
-    self._cpu_metric.Start(page, tab)
-    time.sleep(.5)
-    self._cpu_metric.Stop(page, tab)
-    # Calculate the idle cpu load before any actions are done.
-    self._cpu_metric.AddResults(tab, results,
-                                'idle_cpu_utilization')
+
+    # Measure power usage of tabs after quiescence.
+    util.WaitFor(tab.HasReachedQuiescence, 60)
+
+    self._power_metric.Start(page, tab)
+    time.sleep(5)
+    self._power_metric.Stop(page, tab)
+    self._power_metric.AddResults(tab, results,)
 
     histogram_name = 'MPArch.RWH_TabSwitchPaintDuration'
     histogram_type = histogram_util.BROWSER_HISTOGRAM
     display_name = 'MPArch_RWH_TabSwitchPaintDuration'
     first_histogram = histogram_util.GetHistogram(
         histogram_type, histogram_name, tab)
     prev_histogram = first_histogram
 
     for i in xrange(len(tab.browser.tabs)):
       t = tab.browser.tabs[i]
       t.Activate()
       def _IsDone():
         cur_histogram = histogram_util.GetHistogram(
             histogram_type, histogram_name, tab)
         diff_histogram = histogram_util.SubtractHistogram(
             cur_histogram, prev_histogram)
         return diff_histogram
       util.WaitFor(_IsDone, 30)
       prev_histogram = histogram_util.GetHistogram(
           histogram_type, histogram_name, tab)
 
     last_histogram = histogram_util.GetHistogram(
         histogram_type, histogram_name, tab)
     diff_histogram = histogram_util.SubtractHistogram(last_histogram,
         first_histogram)
 
     results.AddSummary(display_name, '', diff_histogram,
         data_type='unimportant-histogram')