Add MGL entry points and port spinning_cube to use them

mojo/public/c/gpu/GLES2/gl2mojo_autogen.h

Index: mojo/public/c/gpu/GLES2/gl2mojo_autogen.h
diff --git a/gpu/GLES2/gl2chromium_autogen.h b/mojo/public/c/gpu/GLES2/gl2mojo_autogen.h
similarity index 98%
copy from gpu/GLES2/gl2chromium_autogen.h
copy to mojo/public/c/gpu/GLES2/gl2mojo_autogen.h
index a55146139a82d727a7d21f46864036e17eee658d..f153f0541561d4e654511daaf25db004faa09d6f 100644
--- a/gpu/GLES2/gl2chromium_autogen.h
+++ b/mojo/public/c/gpu/GLES2/gl2mojo_autogen.h
@@ -8,10 +8,10 @@
 //    clang-format -i -style=chromium filename
 // DO NOT EDIT!
 
-// This file contains Chromium-specific GLES2 declarations.
+// This file contains Mojo-specific GLES2 declarations.
 
-#ifndef GPU_GLES2_GL2CHROMIUM_AUTOGEN_H_
-#define GPU_GLES2_GL2CHROMIUM_AUTOGEN_H_
+#ifndef GPU_GLES2_GL2MOJO_AUTOGEN_H_
+#define GPU_GLES2_GL2MOJO_AUTOGEN_H_
 
 #define glActiveTexture GLES2_GET_FUN(ActiveTexture)
 #define glAttachShader GLES2_GET_FUN(AttachShader)
@@ -327,4 +327,4 @@
 #define glMatrixLoadIdentityCHROMIUM GLES2_GET_FUN(MatrixLoadIdentityCHROMIUM)
 #define glBlendBarrierKHR GLES2_GET_FUN(BlendBarrierKHR)
 
-#endif  // GPU_GLES2_GL2CHROMIUM_AUTOGEN_H_
+#endif  // GPU_GLES2_GL2MOJO_AUTOGEN_H_