Make webkit_user_agent a standalone gyp

webkit/common/user_agent/webkit_user_agent.gyp

 # Copyright 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.
 
 {
   'targets': [
     {
       'target_name': 'user_agent',
       'type': '<(component)',
       'defines': [
         'WEBKIT_USER_AGENT_IMPLEMENTATION',
       ],
+      'variables': {
+        'chromium_code': 1,
+      },
       'dependencies': [
         '<(DEPTH)/base/base.gyp:base',
         '<(DEPTH)/base/base.gyp:base_i18n',
       ],
       'sources': [
         'user_agent.cc',
         'user_agent.h',
         'user_agent_util.cc',
         'user_agent_util_ios.mm',
         'user_agent_util.h',
@@ skipping 52 matching lines @@
             ],
           },
           # Dependents may rely on files generated by this target or one of its
           # own hard dependencies.
           'hard_dependency': 1,
         },
       ],
     }],
   ],
 }