Generate param traits even when shared by mutliple message files.

content/content_common.gypi

 # 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.
 
 {
   'dependencies': [
     '../base/base.gyp:base',
     '../build/temp_gyp/googleurl.gyp:googleurl',
     '../gpu/gpu.gyp:gles2_implementation',
     '../gpu/gpu.gyp:gpu_ipc',
@@ skipping 321 matching lines @@
     'common/web_database_observer_impl.cc',
     'common/web_database_observer_impl.h',
     'common/webkitplatformsupport_impl.cc',
     'common/webkitplatformsupport_impl.h',
     'common/webmessageportchannel_impl.cc',
     'common/webmessageportchannel_impl.h',
     'common/worker_messages.h',
     'common/zygote_commands_linux.h',
     'public/common/common_param_traits.cc',
     'public/common/common_param_traits.h',
+    'public/common/common_param_traits_macros.h',
     'public/common/content_client.cc',
     'public/common/content_client.h',
     'public/common/window_container_type.cc',
     'public/common/window_container_type.h',
     'public/common/webkit_param_traits.cc',
     'public/common/webkit_param_traits.h',
   ],
   'conditions': [
     ['OS!="win"', {
       'sources!': [
@@ skipping 131 matching lines @@
         '../build/extract_from_cab.py',
         '..\\third_party\\directxsdk\\files\\Redist\\<(input)',
         '<(output)',
         '<(PRODUCT_DIR)',
         ],
       },
      ]
     }]
   ],
 }