Remove all uses of toolkit_use_gtk in the gyp files.

ui/ui_unittests.gyp

 # Copyright 2013 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 221 matching lines @@
                  '../base/allocator/allocator.gyp:allocator',
                ],
             }],
           ],
         }],
         ['use_x11==1', {
           'dependencies': [
             '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
           ],
         }],
-        ['toolkit_uses_gtk == 1', {
-          'sources': [
-            'base/dragdrop/gtk_dnd_util_unittest.cc',
-          ],
-          'dependencies': [
-            '../build/linux/system.gyp:gtk',
-          ],
-        }],
         ['OS=="android" or OS=="ios"', {
           'sources!': [
             'gfx/render_text_unittest.cc',
           ],
         }],
         ['OS!="win" or use_aura==0', {
           'sources!': [
             'base/view_prop_unittest.cc',
           ],
         }],
@@ skipping 84 matching lines @@
           'variables': {
             'test_suite_name': 'ui_unittests',
             'input_shlib_path': '<(SHARED_LIB_DIR)/<(SHARED_LIB_PREFIX)ui_unittests<(SHARED_LIB_SUFFIX)',
           },
           'includes': [ '../build/apk_test.gypi' ],
         },
       ],
     }],
   ],
 }