Telemetry: fix permission check when setting Android command line.

This is to fix a bug introduced by r221426 on the WebView telemetry bot.
The issue was related to the fact that ls -l can return no output if the
target folder exists but is empty.
This change makes the IsProtectedFile logic inside _SetCommandLineFile
more reliable, introducing the IsFileWritableOnDevice method in adb
commands.

BUG=284468
NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/23477053

git-svn-id: http://src.chromium.org/svn/trunk/src/build@222349 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

android/pylib/android_commands.py

@@ -1466,6 +1466,29 @@ class AndroidCommands(object):
 
       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.