Add MGLEcho

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

Index: mojo/public/c/gpu/MGL/mgl_echo.h
diff --git a/mojo/public/c/gpu/MGL/mgl_echo.h b/mojo/public/c/gpu/MGL/mgl_echo.h
new file mode 100644
index 0000000000000000000000000000000000000000..1b9285cbec6d7a1e437cd05e096bf1f39357ebbc
--- /dev/null
+++ b/mojo/public/c/gpu/MGL/mgl_echo.h
@@ -0,0 +1,26 @@
+// 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_