Telemetry: fix permission check when setting Android command line.

build/android/pylib/android_commands.py

 # Copyright (c) 2012 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.
 
 """Provides an interface to communicate with the device via the adb command.
 
 Assumes adb binary is currently on system path.
 """
 
 import collections
@@ skipping 1455 matching lines @@
 
       status = self._adb.SendShellCommand(
           '\'ls "%s" >/dev/null 2>&1; echo $?\'' % (file_name))
       return int(status) == 0
     except ValueError:
       if IsDeviceAttached(self._device):
         raise errors.DeviceUnresponsiveError('Device may be offline.')
 
       return False
 
+  def IsFileWritableOnDevice(self, file_name):
+    """Checks whether the given file (or directory) is writable on the device.
+
+    Args:
+      file_name: Full path of file/directory to check.
+
+    Returns:
+      True if writable, False otherwise.
+    """
+    assert '"' not in file_name, 'file_name cannot contain double quotes'
+    try:
+      status = self._adb.SendShellCommand(
+          '\'test -w "%s"; echo $?\'' % (file_name))
+      if 'test: not found' not in status:
+        return int(status) == 0
+      raise errors.AbortError('"test" binary not found. OS too old.')
+
+    except ValueError:
+      if IsDeviceAttached(self._device):
+        raise errors.DeviceUnresponsiveError('Device may be offline.')
+
+      return False
+
   def TakeScreenshot(self, host_file):
     """Saves a screenshot image to |host_file| on the host.
 
     Args:
       host_file: Absolute path to the image file to store on the host.
     """
     host_dir = os.path.dirname(host_file)
     if not os.path.exists(host_dir):
       os.makedirs(host_dir)
     device_file = '%s/screenshot.png' % self.GetExternalStorage()
@@ skipping 66 matching lines @@
   """
   def __init__(self, output):
     self._output = output
 
   def write(self, data):
     data = data.replace('\r\r\n', '\n')
     self._output.write(data)
 
   def flush(self):
     self._output.flush()