cc: Add missing xdisplaycheck data dependency for tests.

cc/cc_tests.gyp

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
     'cc_unit_tests_source_files': [
       'animation/animation_unittest.cc',
       'animation/keyframed_animation_curve_unittest.cc',
@@ skipping 442 matching lines @@
           'type': 'none',
           'dependencies': [
             'cc_unittests',
           ],
           'includes': [
             '../build/isolate.gypi',
           ],
           'sources': [
             'cc_unittests.isolate',
           ],
+          'conditions': [
+            ['OS=="linux" and use_ozone==0',

[danakj, 2015/03/06 02:30:10]

Can you add a comment for the future, saying what we concluded in this code
review (what GN will have to do, why it is these flags, etc..)?

+              {
+                'dependencies': [
+                  '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
+                ],
+              }
+            ],
+          ],
         },
       ],
     }],
   ],
 }