Refactor ozone drm cursor code for mojo

ui/ozone/platform/drm/gpu/drm_thread.h

Index: ui/ozone/platform/drm/gpu/drm_thread.h
diff --git a/ui/ozone/platform/drm/gpu/drm_thread.h b/ui/ozone/platform/drm/gpu/drm_thread.h
index 56e566d3902b3e3c10321bf4b0a4f16f58b0385b..3dcf284863e3150a3077b32abeb9f40e11f3493c 100644
--- a/ui/ozone/platform/drm/gpu/drm_thread.h
+++ b/ui/ozone/platform/drm/gpu/drm_thread.h
@@ -82,7 +82,8 @@ class DrmThread : public base::Thread {
                  const std::vector<SkBitmap>& bitmaps,
                  const gfx::Point& location,
                  int frame_delay_ms);
-  void MoveCursor(gfx::AcceleratedWidget widget, const gfx::Point& location);
+  void MoveCursor(const gfx::AcceleratedWidget& widget,

[dnicoara, 2016/06/21 14:14:16]

nit: Why const& for AcceleratedWidget? It is supposed to be lightweight.

[rjkroege, 2016/06/21 17:20:52]

To permit the mojo struct traits implementation to be zero-copy, it has to be
const&. You will be seeing more of this for the same reason in subsequent CLs.

[dnicoara, 2016/06/21 17:38:18]

Ah, good to know, thanks for the explanation. Out of curiosity is there a mojo
traits dos/don'ts guide?

+                  const gfx::Point& location);
   void CheckOverlayCapabilities(
       gfx::AcceleratedWidget widget,
       const std::vector<OverlayCheck_Params>& overlays,