Add MGL entry points and port spinning_cube to use them

mojo/public/c/gpu/GLES2/gl2mojo.h

Index: mojo/public/c/gpu/GLES2/gl2mojo.h
diff --git a/gpu/GLES2/gl2chromium.h b/mojo/public/c/gpu/GLES2/gl2mojo.h
similarity index 79%
copy from gpu/GLES2/gl2chromium.h
copy to mojo/public/c/gpu/GLES2/gl2mojo.h
index 0dc648d66086d4bd5cc56b761320d5294a6c7c43..8b259ba3909ef4347bf4328167c8cb5010bf9b72 100644
--- a/gpu/GLES2/gl2chromium.h
+++ b/mojo/public/c/gpu/GLES2/gl2mojo.h
@@ -2,10 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// This file contains Chromium-specific GLES2 declarations.
+// This file contains Mojo-specific GLES2 declarations.
 
-#ifndef GPU_GLES2_GL2CHROMIUM_H_
-#define GPU_GLES2_GL2CHROMIUM_H_
+#ifndef GPU_GLES2_GL2MOJO_H_
+#define GPU_GLES2_GL2MOJO_H_
 
 #include <GLES2/gl2platform.h>
 
@@ -27,7 +27,6 @@
 #endif
 #endif
 
-#include <GLES2/gl2chromium_autogen.h>
-
-#endif  // GPU_GLES2_GL2CHROMIUM_H_
+#include <GLES2/gl2mojo_autogen.h>
 
+#endif  // GPU_GLES2_GL2MOJO_H_