[Telemetry] Add power usage metric

tools/perf/metrics/power.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 logging
+
+from metrics import Metric
+
+
+class PowerMetric(Metric):
+  """A metric for measuring power usage."""
+
+  def __init__(self):
+    super(PowerMetric, self).__init__()
+    self._results = None
+
+  def Start(self, _, tab):
+    if not tab.browser.platform.CanMonitorPowerAsync():
+      logging.warning("System doesn't support async power monitoring.")
+      return
+
+    tab.browser.platform.StartMonitoringPowerAsync()
+
+  def Stop(self, _, tab):
+    if not tab.browser.platform.CanMonitorPowerAsync():
+      return
+
+    self._results = tab.browser.platform.StopMonitoringPowerAsync()
+
+  def AddResults(self, _, results):
+    if not self._results:
+      return
+
+    energy_consumption_mwh = self._results['energy_consumption_mwh']
+    results.Add('energy_consumption_mwh', 'mWh', energy_consumption_mwh)
+    self._results = None