Add MGL entry points and port spinning_cube to use them

shell/native_application_support.cc

Index: shell/native_application_support.cc
diff --git a/shell/native_application_support.cc b/shell/native_application_support.cc
index d3887dcc50ca9bf5a4e5684d0f7489f24de0b6be..f19d3741bcb120df49d5be3e05557789f35a0416 100644
--- a/shell/native_application_support.cc
+++ b/shell/native_application_support.cc
@@ -17,6 +17,8 @@
 #include "mojo/public/platform/native/gles2_impl_oes_vertex_array_object_thunks.h"
 #include "mojo/public/platform/native/gles2_impl_thunks.h"
 #include "mojo/public/platform/native/gles2_thunks.h"
+#include "mojo/public/platform/native/mgl_onscreen_thunks.h"
+#include "mojo/public/platform/native/mgl_thunks.h"
 #include "mojo/public/platform/native/system_impl_private_thunks.h"
 #include "mojo/public/platform/native/system_thunks.h"
 
@@ -105,6 +107,12 @@ bool RunNativeApplication(
     SetThunks(MojoMakeGLES2ImplChromiumTextureMailboxThunks,
               "MojoSetGLES2ImplChromiumTextureMailboxThunks", app_library);
   }
+  SetThunks(MojoMakeMGLThunks, "MojoSetMGLThunks", app_library);

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

I suppose the conditional for the GLES2 control thunks would eventually be
replaced by this eventually?

(It's a little awkward[*] to add this to the conditional above, since you'd
really want a non-short-circuiting logical or, which is a bit weird.)

[*] Also a little wrong, since conceivably you might want MGL without the GLES2
impl (e.g., if you want GLES3).

Maybe add a TODO or something like that?

[jamesr, 2015/08/13 19:42:27]

I made the MGL onscreen thunks conditional on the MGL thunks but made the rest
unconditional (so an app can get the GLES2 impl thunks without the GLES2 control
thunks, which it needs to make GL calls on a context it creates with MGL.  I'm
not sure having any of these be conditional makes a lot of sense

+
+  // TODO(jamesr): We should only need to expose these on apps that need to draw
+  // to the screen like the system compositor.
+  SetThunks(MojoMakeMGLOnscreenThunks, "MojoSetMGLOnscreenThunks", app_library);

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

And presumably this would also be conditional on there being the basic MGL
thunks....

+
   // Unlike system thunks, we don't warn on a lack of GLES2 thunks because
   // not everything is a visual app.