[telemetry] Add IPPET power monitor.

tools/telemetry/telemetry/core/platform/mac_platform_backend.py

Index: tools/telemetry/telemetry/core/platform/mac_platform_backend.py
diff --git a/tools/telemetry/telemetry/core/platform/mac_platform_backend.py b/tools/telemetry/telemetry/core/platform/mac_platform_backend.py
index 368d9b10915967b585150a1a83d9b2dc6b89ecf5..c83f5a754909366ba3ef13f8f1aeffda9ff2e037 100644
--- a/tools/telemetry/telemetry/core/platform/mac_platform_backend.py
+++ b/tools/telemetry/telemetry/core/platform/mac_platform_backend.py
@@ -20,7 +20,7 @@ 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):
@@ -152,13 +152,13 @@ class MacPlatformBackend(posix_platform_backend.PosixPlatformBackend):
     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()