[Android] Enable root in perf_control.SetHighPerfMode.

build/android/pylib/perf/perf_control.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 atexit
 import logging
 
 from pylib import android_commands
+from pylib.device import device_errors
 from pylib.device import device_utils
 
+
 class PerfControl(object):
   """Provides methods for setting the performance mode of a device."""
   _CPU_PATH = '/sys/devices/system/cpu'
   _KERNEL_MAX = '/sys/devices/system/cpu/kernel_max'
 
   def __init__(self, device):
     # TODO(jbudorick) Remove once telemetry gets switched over.
     if isinstance(device, android_commands.AndroidCommands):
       device = device_utils.DeviceUtils(device)
     self._device = device
     # this will raise an AdbCommandFailedError if no CPU files are found
     self._cpu_files = self._device.RunShellCommand(
         'ls -d cpu[0-9]*', cwd=self._CPU_PATH, check_return=True, as_root=True)
     assert self._cpu_files, 'Failed to detect CPUs.'
     self._cpu_file_list = ' '.join(self._cpu_files)
     logging.info('CPUs found: %s', self._cpu_file_list)
     self._have_mpdecision = self._device.FileExists('/system/bin/mpdecision')
 
   def SetHighPerfMode(self):
     """Sets the highest stable performance mode for the device."""
-    if not self._device.HasRoot():
+    try:
+      self._device.EnableRoot()
+    except device_errors.CommandFailedError:
       message = 'Need root for performance mode. Results may be NOISY!!'
       logging.warning(message)
       # Add an additional warning at exit, such that it's clear that any results
       # may be different/noisy (due to the lack of intended performance mode).
       atexit.register(logging.warning, message)
       return
 
     product_model = self._device.product_model
     # TODO(epenner): Enable on all devices (http://crbug.com/383566)
     if 'Nexus 4' == product_model:
@@ skipping 106 matching lines @@
     """
     if self._have_mpdecision:
       script = 'stop mpdecision' if force_online else 'start mpdecision'
       self._device.RunShellCommand(script, check_return=True, as_root=True)
 
     if not self._have_mpdecision and not self._AllCpusAreOnline():
       logging.warning('Unexpected cpu hot plugging detected.')
 
     if force_online:
       self._ForEachCpu('echo 1 > "$CPU/online"')