ozone: Add overlay candidate implementation that queries support via IPC

ui/ozone/public/overlay_candidates_ozone.h

Index: ui/ozone/public/overlay_candidates_ozone.h
diff --git a/ui/ozone/public/overlay_candidates_ozone.h b/ui/ozone/public/overlay_candidates_ozone.h
index c5733300491ebddc0ba05e689b82016c36c4a878..2ae0d127f7fbc1285bde033725fd4963bb8d2891 100644
--- a/ui/ozone/public/overlay_candidates_ozone.h
+++ b/ui/ozone/public/overlay_candidates_ozone.h
@@ -27,6 +27,8 @@ class OZONE_BASE_EXPORT OverlayCandidatesOzone {
     gfx::OverlayTransform transform;
     // Format of the buffer to composite.
     SurfaceFactoryOzone::BufferFormat format;
+    // Size of the buffer, in pixels.
+    gfx::Size buffer_size;
     // Rect on the display to position the overlay to. Input rectangle may
     // not have integer coordinates, but when accepting for overlay, must
     // be modified by CheckOverlaySupport to output integer values.