Prefer Khronos EGL headers instead Mesa for all OS

ui/gl/gl.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,
   },
 
   'targets': [
@@ skipping 11 matching lines @@
         '<(DEPTH)/ui/gfx/gfx.gyp:gfx_geometry',
       ],
       'variables': {
         'gl_binding_output_dir': '<(SHARED_INTERMEDIATE_DIR)/ui/gl',
       },
       'defines': [
         'GL_IMPLEMENTATION',
       ],
       'include_dirs': [
         '<(DEPTH)/third_party/swiftshader/include',
+        '<(DEPTH)/third_party/khronos',
         '<(DEPTH)/third_party/mesa/src/include',

[no sievers, 2014/02/28 20:53:26]

Can we remove mesa here?

We already specify the explicit path where we need additional headers, such as
in gl_surface_x11.cc:
#include "third_party/mesa/src/include/GL/osmesa.h"

[Ken Russell (switch to Gerrit), 2014/02/28 21:25:04]

I don't know -- a try job would be needed. In general I think the answer is no,
though. The OpenGL and OpenGL ES headers themselves refer to paths like
<GL/gl.h> and <KHR/khrplatform.h>.

         '<(gl_binding_output_dir)',
       ],
       'direct_dependent_settings': {
         'include_dirs': [
           '<(gl_binding_output_dir)',
         ],
       },
       'export_dependent_settings': [
         '<(DEPTH)/third_party/mesa/mesa.gyp:mesa_headers',
       ],
@@ skipping 310 matching lines @@
           'variables': {
             'jni_gen_package': 'ui/gl',
             'jni_generator_ptr_type': 'long',
           },
           'includes': [ '../../build/jni_generator.gypi' ],
         },
       ],
     }],
   ],
 }