[Android] Make cmdline_file argument to FlagChanger mandatory.

build/android/pylib/uiautomator/test_runner.py

 # Copyright (c) 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.
 
 """Class for running uiautomator tests on a single device."""
 
 from pylib import constants
 from pylib.instrumentation import test_options as instr_test_options
 from pylib.instrumentation import test_runner as instr_test_runner
 
@@ skipping 36 matching lines @@
   def InstallTestPackage(self):
     self.test_pkg.Install(self.adb)
 
   #override
   def PushDataDeps(self):
     pass
 
   #override
   def _RunTest(self, test, timeout):
     self.adb.ClearApplicationState(self._package)
-    if 'Feature:FirstRunExperience' in self.test_pkg.GetTestAnnotations(test):
-      self.flags.RemoveFlags(['--disable-fre'])
-    else:
-      self.flags.AddFlags(['--disable-fre'])
+    if self.flags:
+      if 'Feature:FirstRunExperience' in self.test_pkg.GetTestAnnotations(test):
+        self.flags.RemoveFlags(['--disable-fre'])
+      else:
+        self.flags.AddFlags(['--disable-fre'])
     self.adb.StartActivity(self._package,
                            self._activity,
                            wait_for_completion=True,
                            action='android.intent.action.MAIN',
                            force_stop=True)
     return self.adb.RunUIAutomatorTest(
         test, self.test_pkg.GetPackageName(), timeout)