[Telemetry] Shortcut 30s energy measurement if not supported.

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 44 matching lines @@
 
   def ValidateAndMeasurePage(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
 
     # Measure power usage of tabs after quiescence.
     util.WaitFor(tab.HasReachedQuiescence, 60)
 
-    self._power_metric.Start(page, tab)
-    time.sleep(TabSwitching.SAMPLE_TIME)
-    self._power_metric.Stop(page, tab)
-    self._power_metric.AddResults(tab, results,)
+    if tab.browser.platform.CanMonitorPower():
+      self._power_metric.Start(page, tab)
+      time.sleep(TabSwitching.SAMPLE_TIME)
+      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]
@@ skipping 10 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))