Add MGLEcho

mojo/public/c/gpu/MGL/mgl_echo.h

+// Copyright 2016 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.
+
+// Note: This header should be compilable as C.
+
+#ifndef MOJO_PUBLIC_C_GPU_MGL_MGL_ECHO_H_
+#define MOJO_PUBLIC_C_GPU_MGL_MGL_ECHO_H_
+
+#include <stdint.h>
+
+#include "mojo/public/c/gpu/MGL/mgl_types.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef void (*MGLEchoCallback)(void* closure);
+
+void MGLEcho(MGLEchoCallback callback, void* closure);
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // MOJO_PUBLIC_C_GPU_MGL_MGL_ECHO_H_