Added switch to disable specified GL extensions.

ui/gl/gl_tests.gyp

 # Copyright 2015 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': [
     {
       'target_name': 'gl_unittests',
       'type': '<(gtest_target_type)',
       'sources': [
         'test/run_all_unittests.cc',
+        'gl_api_unittest.cc',
       ],
       'dependencies': [
         '<(DEPTH)/base/base.gyp:base',
         '<(DEPTH)/base/base.gyp:test_support_base',
         '<(DEPTH)/testing/gtest.gyp:gtest',
+        'gl.gyp:gl',
       ],
       'conditions': [
         ['OS == "android"', {
           'dependencies': [
             '<(DEPTH)/testing/android/native_test.gyp:native_test_native_code',
           ],
         }],
       ],
     }
   ],
@@ skipping 32 matching lines @@
               'dependencies': [
                 '<(DEPTH)/tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
               ],
             }],
           ],
         },
       ],
     }],
   ],
 }