Support for TakeScreenshot in cros_platform.

telemetry/telemetry/internal/platform/cros_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 logging
 
 from telemetry import decorators
 from telemetry.core import cros_interface
 from telemetry.core import platform
 from telemetry.core import util
@@ skipping 149 matching lines @@
     self._powermonitor.StartMonitoringPower(browser)
 
   def StopMonitoringPower(self):
     return self._powermonitor.StopMonitoringPower()
 
   def PathExists(self, path, timeout=None, retries=None):
     if timeout or retries:
       logging.warning(
           'PathExists: params timeout and retries are not support on CrOS.')
     return self._cri.FileExistsOnDevice(path)
+
+  def CanTakeScreenshot(self):
+    return True
+
+  def TakeScreenshot(self, file_path):
+    self._cri.TakeScreenshot(file_path)

[nednguyen, 2016/04/06 23:20:19]

this return True if it's believed the attempt succeeded.