Add a basic NativeViewportMac for Mojo

ui/gl/gl_context_mac.mm

Index: ui/gl/gl_context_mac.mm
diff --git a/ui/gl/gl_context_mac.mm b/ui/gl/gl_context_mac.mm
index 4233fe8618925ceb9da12bde61f289fe9af819b5..5a497cda47d0c8b92fcb77ab1659351826f1e278 100644
--- a/ui/gl/gl_context_mac.mm
+++ b/ui/gl/gl_context_mac.mm
@@ -8,16 +8,13 @@
 #include "base/memory/scoped_ptr.h"
 #include "third_party/mesa/src/include/GL/osmesa.h"
 #include "ui/gl/gl_context_cgl.h"
+#include "ui/gl/gl_context_nsview.h"
 #include "ui/gl/gl_context_osmesa.h"
 #include "ui/gl/gl_context_stub.h"
 #include "ui/gl/gl_implementation.h"
 #include "ui/gl/gl_surface.h"
 #include "ui/gl/gl_switches.h"
 
-#if defined(USE_AURA)
-#include "ui/gl/gl_context_nsview.h"
-#endif
-
 namespace gfx {
 
 class GLShareGroup;
@@ -31,14 +28,10 @@ scoped_refptr<GLContext> GLContext::CreateGLContext(
     case kGLImplementationDesktopGL:
     case kGLImplementationAppleGL: {
       scoped_refptr<GLContext> context;
-#if defined(USE_AURA)
       if (compatible_surface->IsOffscreen())
         context = new GLContextCGL(share_group);
       else
         context = new GLContextNSView(share_group);
-#else
-      context = new GLContextCGL(share_group);
-#endif // USE_AURA
       if (!context->Initialize(compatible_surface, gpu_preference))
         return NULL;