Update gl2.h and gl2ext.h headers from Khronos.

ppapi/lib/gl/gles2/gles2.c

 // 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.
 
 // This file is auto-generated from
 // gpu/command_buffer/build_gles2_cmd_buffer.py
 // DO NOT EDIT!
 
 #include <GLES2/gl2.h>
+#include <GLES2/gl2ext.h>
 #include "ppapi/lib/gl/gles2/gl2ext_ppapi.h"
 
 void GL_APIENTRY glActiveTexture(GLenum texture) {
   glGetInterfacePPAPI()->ActiveTexture(glGetCurrentContextPPAPI(), texture);
 }
 
 void GL_APIENTRY glAttachShader(GLuint program, GLuint shader) {
   glGetInterfacePPAPI()->AttachShader(
       glGetCurrentContextPPAPI(), program, shader);
 }
@@ skipping 862 matching lines @@
         glGetCurrentContextPPAPI(), mode, count, type, indices, primcount);
 }
 
 void GL_APIENTRY glVertexAttribDivisorANGLE(GLuint index, GLuint divisor) {
   const struct PPB_OpenGLES2InstancedArrays_Dev* ext =
       glGetInstancedArraysInterfacePPAPI();
   if (ext)
     ext->VertexAttribDivisorANGLE(glGetCurrentContextPPAPI(), index, divisor);
 }