Telemetry: fix permission check when setting Android command line.

tools/telemetry/telemetry/core/backends/chrome/android_browser_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
 import os
 import subprocess
 import sys
 import time
 
@@ skipping 189 matching lines @@
 
     args = [self._backend_settings.pseudo_exec_name]
     args.extend(self.GetBrowserStartupArgs())
     args = ' '.join(map(QuoteIfNeeded, args))
 
     self._SetCommandLineFile(args)
 
   def _SetCommandLineFile(self, file_contents):
     def IsProtectedFile(name):
       if self._adb.Adb().FileExistsOnDevice(name):
-        ls_output = self._adb.RunShellCommand('ls -l %s' % name)[0]
-        return ls_output == 'opendir failed, Permission denied' or \
-            ls_output.split()[1] == 'root'
+        return not self._adb.Adb().IsFileWritableOnDevice(name)
       else:
         parent_name = os.path.dirname(name)
         if parent_name != '':
           return IsProtectedFile(parent_name)
         else:
           return True
 
     if IsProtectedFile(self._backend_settings.cmdline_file):
       if not self._adb.Adb().CanAccessProtectedFileContents():
         logging.critical('Cannot set Chrome command line. '
@@ skipping 130 matching lines @@
       forwarder.SetPorts(*port_pairs)
       assert self.WEBPAGEREPLAY_HOST == forwarder.host_ip, (
         'Host IP address on the RNDIS interface changed. Must restart browser!')
       if self._override_dns:
         forwarder.OverrideDns()
       return forwarder
     assert not self._override_dns, ('The user-space forwarder does not support '
                                     'DNS override!')
     logging.warning('Using the user-space forwarder.\n')
     return adb_commands.Forwarder(self._adb, *port_pairs)