Add MGLEcho

mojo/public/platform/native/mgl_echo_thunks.c

+// 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.
+
+#include "mojo/public/platform/native/mgl_echo_thunks.h"
+
+#include <assert.h>
+
+#include "mojo/public/platform/native/thunk_export.h"
+
+static struct MGLEchoThunks g_echo_thunks = {0};
+
+void MGLEcho(MGLEchoCallback callback, void* closure) {
+  assert(g_echo_thunks.MGLEcho);
+  g_echo_thunks.MGLEcho(callback, closure);
+}
+
+THUNK_EXPORT size_t MojoSetMGLEchoThunks(
+    const struct MGLEchoThunks* mgl_echo_thunks) {
+  if (mgl_echo_thunks->size >= sizeof(g_echo_thunks))
+    g_echo_thunks = *mgl_echo_thunks;
+  return sizeof(g_echo_thunks);
+}