[Android] Enable root in perf_control.SetHighPerfMode.

build/android/pylib/perf/perf_control.py

Index: build/android/pylib/perf/perf_control.py
diff --git a/build/android/pylib/perf/perf_control.py b/build/android/pylib/perf/perf_control.py
index b6a0989eb9f052c7e54459f7b0e1e725d54b90a3..f89f397d24e2930f54a8d737aeb54166912555e4 100644
--- a/build/android/pylib/perf/perf_control.py
+++ b/build/android/pylib/perf/perf_control.py
@@ -6,8 +6,10 @@ 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'
@@ -28,7 +30,9 @@ class PerfControl(object):
 
   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