Add a basic NativeViewportMac for Mojo

ui/gl/gl_surface_nsview.h

Index: ui/gl/gl_surface_nsview.h
diff --git a/ui/gl/gl_surface_nsview.h b/ui/gl/gl_surface_nsview.h
index 8344839771eccbd90ba8442fd89148cc96e91511..5562ca106abf538c983855e73bf34cb84f656e1a 100644
--- a/ui/gl/gl_surface_nsview.h
+++ b/ui/gl/gl_surface_nsview.h
@@ -16,10 +16,9 @@ class GLContextNSView;
 // GLSurfaceNSView provides an implementation of the the GLSurface interface
 // that is backed by an NSView.  This interface pairs with the GLContextNSView
 // class, and the NSView is expected to use this context for drawing.
-class GLSurfaceNSView : public GLSurface {
+class GL_EXPORT GLSurfaceNSView : public GLSurface {
  public:
   explicit GLSurfaceNSView(AcceleratedWidget view);
-  virtual ~GLSurfaceNSView();
 
   // GLSurface:
   virtual void Destroy() OVERRIDE;
@@ -32,6 +31,8 @@ class GLSurfaceNSView : public GLSurface {
   virtual bool OnMakeCurrent(GLContext* context) OVERRIDE;
 
  private:
+  virtual ~GLSurfaceNSView();
+
   // Weak.  An |NSView*|.
   AcceleratedWidget view_;