Make async waiter explicit MojoGLES2CreateContext param

mojo/public/cpp/gles2/gles2.h

-// Copyright 2014 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_PUBLIC_CPP_GLES2_GLES2_H_
-#define MOJO_PUBLIC_CPP_GLES2_GLES2_H_
-
-#include "mojo/public/c/gles2/gles2.h"
-#include "mojo/public/cpp/environment/environment.h"
-
-namespace mojo {
-
-class GLES2Initializer {
- public:
-  explicit GLES2Initializer(const MojoAsyncWaiter* async_waiter =
-                                Environment::GetDefaultAsyncWaiter()) {
-    MojoGLES2Initialize(async_waiter);
-  }
-  ~GLES2Initializer() { MojoGLES2Terminate(); }
-};
-
-}  // namespace mojo
-
-#endif  // MOJO_PUBLIC_CPP_GLES2_GLES2_H_