Add GetProcAddress to OpenGL control interface

mojo/gles2/control_thunks_impl.h

 // Copyright 2015 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.
 
 #ifndef MOJO_GLES2_CONTROL_THUNKS_IMPL_H_
 #define MOJO_GLES2_CONTROL_THUNKS_IMPL_H_
 
 #include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/threading/thread_local.h"
@@ skipping 27 matching lines @@
   void DestroyContext(MGLContext context);
 
   void MakeCurrent(MGLContext context);
 
   MGLContext GetCurrentContext();
 
   void ResizeSurface(uint32_t width, uint32_t height);
 
   void SwapBuffers();
 
+  MGLMustCastToProperFunctionPointerType GetProcAddress(const char* procname);
+
   void* GetGLES2Interface(MGLContext context);
 
   void SignalSyncPoint(uint32_t sync_point,
                        MGLSignalSyncPointCallback callback,
                        void* closure);
 
   gpu::gles2::GLES2Interface* CurrentGLES2Interface();
 
  private:
   friend base::DefaultLazyInstanceTraits<gles2::ControlThunksImpl>;
   ControlThunksImpl();
   ~ControlThunksImpl();
 
   base::ThreadLocalPointer<GLES2Context> current_context_tls_;
 
   DISALLOW_COPY_AND_ASSIGN(ControlThunksImpl);
 };
 
 }  // namespace gles2
 
 #endif  // MOJO_GLES2_CONTROL_THUNKS_IMPL_H_