mac: Fix build with 10.9 SDK (from Xcode 6).

content/browser/compositor/io_surface_layer_mac.mm

 // 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.
 
 #include "content/browser/compositor/io_surface_layer_mac.h"
 
 #include <sstream>
 
 #include <CoreFoundation/CoreFoundation.h>
 #include <OpenGL/CGLIOSurface.h>
 #include <OpenGL/CGLRenderers.h>
+#include <OpenGL/gl.h>
 #include <OpenGL/OpenGL.h>
 
 #include "base/mac/mac_util.h"
 #include "base/mac/sdk_forward_declarations.h"
 #include "content/browser/gpu/gpu_data_manager_impl.h"
 #include "content/browser/renderer_host/render_widget_host_impl.h"
 #include "content/browser/renderer_host/render_widget_host_view_mac.h"
 #include "ui/base/cocoa/animation_utils.h"
 #include "ui/gfx/size_conversions.h"
 #include "ui/gl/scoped_cgl.h"
@@ skipping 468 matching lines @@
                  io_surface_texture_));
 
   // Reset the texture state.
   io_surface_texture_ = 0;
   io_surface_texture_context_.reset();
   io_surface_texture_io_surface_.reset();
   cgl_renderer_id_ = 0;
 }
 
 @end