Telemetry: fix AndroidBrowserFinderTest.

tools/telemetry/telemetry/system_stub.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 stubs for os, sys and subprocess for testing
 
 This test allows one to test code that itself uses os, sys, and subprocess.
 """
 
 import os
 import re
@@ skipping 58 matching lines @@
     self.AdbCommands = AdbCommandsStubConstructor
 
   @staticmethod
   def IsAndroidSupported():
     return True
 
   def GetAttachedDevices(self):
     return self.attached_devices
 
   @staticmethod
-  def HasForwarder(_):
+  def HasForwarder(_=None):
     return True
 
 class OsModuleStub(object):
   class OsPathModuleStub(object):
     def __init__(self, sys_module):
       self.sys = sys_module
       self.files = []
 
     def exists(self, path):
       return path in self.files
@@ skipping 55 matching lines @@
   def __init__(self):
     self.Popen = SubprocessModuleStub.PopenStub()
     self.PIPE = None
 
   def call(self, *args, **kwargs):
     raise NotImplementedError()
 
 class SysModuleStub(object):
   def __init__(self):
     self.platform = ''