[Android] Switch to DeviceUtils versions of file functions.

tools/telemetry/telemetry/core/platform/power_monitor/android_ds2784_power_monitor.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
 import os
 
 from telemetry import decorators
 from telemetry.core.platform.profiler import android_prebuilt_profiler_helper
 import telemetry.core.platform.power_monitor as power_monitor
@@ skipping 11 matching lines @@
   def __init__(self, device):
     super(DS2784PowerMonitor, self).__init__()
     self._device = device
     self._powermonitor_process_port = None
     self._file_poller_binary = android_prebuilt_profiler_helper.GetDevicePath(
         'file_poller')
 
 
   @decorators.Cache
   def _HasFuelGauge(self):
-    return self._device.old_interface.FileExistsOnDevice(CHARGE_COUNTER)
+    return self._device.FileExists(CHARGE_COUNTER)
 
   def CanMonitorPower(self):
     if not self._HasFuelGauge():
       return False
     if self._device.old_interface.IsDeviceCharging():
       logging.warning('Can\'t monitor power usage since device is charging.')
       return False
     return True
 
   def StartMonitoringPower(self, browser):
@@ skipping 76 matching lines @@
     total_energy_consumption_mwh += remaining_energy_consumption_mwh
 
     # -------- Collect and Process Data -------------
     out_dict = {}
     # Raw power usage samples.
     out_dict['identifier'] = 'ds2784'
     out_dict['power_samples_mw'] = power_samples
     out_dict['energy_consumption_mwh'] = total_energy_consumption_mwh
 
     return out_dict