[Ozone] Fix SingleOnTop issue by checking if the quad is clipped.

cc/output/overlay_candidate.h

Index: cc/output/overlay_candidate.h
diff --git a/cc/output/overlay_candidate.h b/cc/output/overlay_candidate.h
index b3e7fb359f19e4b7e6a1d15ace9f5cc3046c97c9..2154c865258a7bac8d5d9fc02620d087350ca70f 100644
--- a/cc/output/overlay_candidate.h
+++ b/cc/output/overlay_candidate.h
@@ -41,6 +41,13 @@ class CC_EXPORT OverlayCandidate {
   gfx::RectF display_rect;
   // Crop within the buffer to be placed inside |display_rect|.
   gfx::RectF uv_rect;
+
+  // Original visible area of the quad

[danakj, 2015/08/28 22:48:10]

period at the end

can you explain what you mean by original vs actual? original before what?
actual is after what?

I think these names may be misleading. One is the visible rect in the quad. One
is the visible bounds of the layer the quad came from. They are not even in the
same coordinate space, one is in layer space, one is in quad geometry space.

[william.xie1, 2015/08/28 23:18:42]

Hi Dana,
 Thanks for your comments.
My previous meaning is, original means before composition, actual means after
composition. From my testing, original rect doesn not change, it only reply on
the page scaling factor. Actual rect will change to the actual visible rect if
the quad is clipped.

So it is workable by comparing these two rects to decide if quad is clipped.
Do you agree on this?
also, do you think we should find good names to describe these two rects?

+  gfx::Rect original_visible_rect;
+
+  // Actual visible area of the quad

[danakj, 2015/08/28 22:48:09]

ditto

+  gfx::Rect actual_visible_rect;
+
   // Texture resource to present in an overlay.
   unsigned resource_id;
   // Stacking order of the overlay plane relative to the main surface,