Make the gyp files more cross-platform across the Unices

content/content_plugin.gypi

 # Copyright (c) 2011 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': 'content_plugin',
       'type': '<(library)',
       'msvs_guid': '20A560A0-2CD0-4D9E-A58B-1F24B99C087A',
@@ skipping 36 matching lines @@
         'plugin/webplugin_proxy.h',
       ],
       # These are layered in conditionals in the event other platforms
       # end up using this module as well.
       'conditions': [
         ['OS=="win"', {
           'include_dirs': [
             '<(DEPTH)/third_party/wtl/include',
           ],
         }],
-        ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="solaris"', {
+        ['toolkit_uses_gtk==1', {
           'dependencies': [
             '../build/linux/system.gyp:gtk',
           ],
         }],
       ],
     },
   ],
 }