gpu: Add calling convention for win32

gpu/command_buffer/client/gles2_lib.h

 // 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.
 
 // These functions emulate GLES2 over command buffers.
 
 #ifndef GPU_COMMAND_BUFFER_CLIENT_GLES2_LIB_H_
 #define GPU_COMMAND_BUFFER_CLIENT_GLES2_LIB_H_
 
 #include "gpu/command_buffer/client/gles2_c_lib_export.h"
 #include "gpu/command_buffer/client/gles2_interface.h"
 
 namespace gles2 {
 
-typedef void (*GLES2FunctionPointer)(void);
+typedef void(GL_APIENTRY* GLES2FunctionPointer)(void);
 
 struct NameToFunc {
   const char* name;
   gles2::GLES2FunctionPointer func;
 };
 
 // Initialize the GLES2 library.
 GLES2_C_LIB_EXPORT void Initialize();
 
 // Terminate the GLES2 library.
 GLES2_C_LIB_EXPORT void Terminate();
 
 // Get the current GL context.
 GLES2_C_LIB_EXPORT gpu::gles2::GLES2Interface* GetGLContext();
 
 // Set the current GL context.
 GLES2_C_LIB_EXPORT void SetGLContext(gpu::gles2::GLES2Interface* impl);
 
 GLES2_C_LIB_EXPORT GLES2FunctionPointer GetGLFunctionPointer(const char* name);
 
 }  // namespace gles2
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_GLES2_LIB_H_