GLContextNSView should not assume concrete type GLSurface is GLSurfaceNSView

ui/gfx/gl/gl_context_mac.mm

Index: ui/gfx/gl/gl_context_mac.mm
diff --git a/ui/gfx/gl/gl_context_mac.mm b/ui/gfx/gl/gl_context_mac.mm
index adf67aa747e1e34a0a307a6e086338cf5653ee2c..2fcd085c304c2a4291e430c7856b676b36466f48 100644
--- a/ui/gfx/gl/gl_context_mac.mm
+++ b/ui/gfx/gl/gl_context_mac.mm
@@ -43,15 +43,15 @@ scoped_refptr<GLContext> GLContext::CreateGLContext(
     case kGLImplementationDesktopGL: {
       scoped_refptr<GLContext> context;
 #if defined(USE_AURA)
-      DCHECK(!compatible_surface->IsOffscreen());
-      context = new GLContextNSView(share_group);
-      if (!context->Initialize(compatible_surface, gpu_preference))
-        return NULL;
+      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;
-#endif // USE_AURA
 
       return context;
     }