Refactor decorators into thier own python class

tools/chrome_proxy/webdriver/decorator_smoke.py

 # Copyright 2017 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.
 
-from common import AndroidOnly
+from decorators import AndroidOnly
 from common import ParseFlags
 from common import IntegrationTest
 
 
 class DecoratorSmokeTest(IntegrationTest):
 
   def AndroidOnlyFunction(self):
     # This function should never be called.
     self.fail()
 
   @AndroidOnly
   def testDecorator(self):
     # This test should always result as 'skipped' or pass if --android given.
     if not ParseFlags().android:
       self.AndroidOnlyFunction()
 
 
 if __name__ == '__main__':
   IntegrationTest.RunAllTests()