[telemetry] Add IPPET power monitor.

tools/telemetry/telemetry/core/platform/mac_platform_backend.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.
 
 import ctypes
 import os
 import time
 try:
   import resource  # pylint: disable=F0401
 except ImportError:
   resource = None  # Not available on all platforms
 
 from telemetry import decorators
 from telemetry.core.platform import platform_backend
 from telemetry.core.platform import posix_platform_backend
 from telemetry.core.platform.power_monitor import powermetrics_power_monitor
 
 
 class MacPlatformBackend(posix_platform_backend.PosixPlatformBackend):
   def __init__(self):
     super(MacPlatformBackend, self).__init__()
     self.libproc = None
-    self.power_monitor_ = powermetrics_power_monitor.PowerMetricsPowerMonitor(
+    self._power_monitor = powermetrics_power_monitor.PowerMetricsPowerMonitor(
         self)
 
   def StartRawDisplayFrameRateMeasurement(self):
     raise NotImplementedError()
 
   def StopRawDisplayFrameRateMeasurement(self):
     raise NotImplementedError()
 
   def GetRawDisplayFrameRateMeasurements(self):
     raise NotImplementedError()
@@ skipping 111 matching lines @@
   def CanFlushIndividualFilesFromSystemCache(self):
     return False
 
   def FlushEntireSystemCache(self):
     mavericks_or_later = self.GetOSVersionName() >= platform_backend.MAVERICKS
     p = self.LaunchApplication('purge', elevate_privilege=mavericks_or_later)
     p.communicate()
     assert p.returncode == 0, 'Failed to flush system cache'
 
   def CanMonitorPower(self):
-    return self.power_monitor_.CanMonitorPower()
+    return self._power_monitor.CanMonitorPower()
 
   def CanMeasurePerApplicationPower(self):
-    return self.power_monitor_.CanMeasurePerApplicationPower()
+    return self._power_monitor.CanMeasurePerApplicationPower()
 
   def StartMonitoringPower(self, browser):
-    self.power_monitor_.StartMonitoringPower(browser)
+    self._power_monitor.StartMonitoringPower(browser)
 
   def StopMonitoringPower(self):
-    return self.power_monitor_.StopMonitoringPower()
+    return self._power_monitor.StopMonitoringPower()