Disable UI compositor partial swaps on Mac

There isn't a mechanism for doing partial swaps of a CAOpenGLLayer
on Mac.

BUG=314190

Review URL: https://codereview.chromium.org/316173005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@275469 0039d316-1c4b-4281-b951-d872f2087c98

ui/compositor/compositor.cc

@@ -100,8 +100,10 @@ Compositor::Compositor(gfx::AcceleratedWidget widget,
   settings.main_frame_before_activation_enabled = false;
   settings.throttle_frame_production =
       !command_line->HasSwitch(switches::kDisableGpuVsync);
+#if !defined(OS_MACOSX)
   settings.partial_swap_enabled =
       !command_line->HasSwitch(cc::switches::kUIDisablePartialSwap);
+#endif
 #if defined(OS_CHROMEOS)
   settings.per_tile_painting_enabled = true;
 #endif