Add MGL entry points and port spinning_cube to use them

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

Index: mojo/public/c/gpu/MGL/mgl_onscreen.h
diff --git a/mojo/public/c/gpu/MGL/mgl_onscreen.h b/mojo/public/c/gpu/MGL/mgl_onscreen.h
new file mode 100644
index 0000000000000000000000000000000000000000..407af7fbb893c603e577acd906a0e2ab7e020d0f
--- /dev/null
+++ b/mojo/public/c/gpu/MGL/mgl_onscreen.h
@@ -0,0 +1,27 @@
+// 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_PUBLIC_C_GPU_MGL_MGL_ONSCREEN_H_
+#define MOJO_PUBLIC_C_GPU_MGL_MGL_ONSCREEN_H_
+
+#include <stdint.h>
+
+#include "mojo/public/c/gpu/MGL/mgl_types.h"
+// Note: This header should be compilable as C.

[viettrungluu, 2015/08/12 02:48:10]

nit: I think I prefer this comment to be above the include guards.

Also, blank line between <stuff> and the #ifdef __cplusplus below.

+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Resizes the default framebuffer for the currently bound onscreen MGLContext.
+void MGLResizeSurface(uint32_t width, uint32_t height);
+
+// Presents the default framebuffer for the currently bound onscreen MGLContext
+// to the windowing system or display.
+void MGLSwapBuffers();
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // MOJO_PUBLIC_C_GPU_MGL_MGL_ONSCREEN_H_