Move GL one-off initialization code.

ui/gl/init/gl_init.gyp

 # Copyright 2016 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_init',
       'type': '<(component)',
       'dependencies': [
         '../../../base/base.gyp:base',
         '../../gfx/gfx.gyp:gfx',
         '../../gfx/gfx.gyp:gfx_geometry',
         '../gl.gyp:gl',
       ],
       'defines': [
         'GL_INIT_IMPLEMENTATION',
       ],
       'sources': [
+        'gl_initializer.h',
+        'gl_initializer_android.cc',
+        'gl_initializer_mac.cc',
+        'gl_initializer_ozone.cc',
+        'gl_initializer_win.cc',
+        'gl_initializer_x11.cc',
         'gl_factory.cc',
         'gl_factory.h',
         'gl_init_export.h',
       ],
+      'conditions': [
+        ['OS=="mac"', {
+          'link_settings': {
+            'libraries': [
+              '$(SDKROOT)/System/Library/Frameworks/OpenGL.framework',
+            ],
+          },
+        }],
+      ],
     },
   ],
 }