Use SwapBuffersWithBounds on Chromecast

cc/output/output_surface_frame.h

Index: cc/output/output_surface_frame.h
diff --git a/cc/output/output_surface_frame.h b/cc/output/output_surface_frame.h
index 2306f2e5b4bbe686807d324dd438eee65266d245..a2437c2f51cd3bd59c051bdb7f5d9f5f50208170 100644
--- a/cc/output/output_surface_frame.h
+++ b/cc/output/output_surface_frame.h
@@ -26,7 +26,12 @@ class CC_EXPORT OutputSurfaceFrame {
   OutputSurfaceFrame& operator=(OutputSurfaceFrame&& other);
 
   gfx::Size size;
+  // |sub_buffer_rect| = swap rect for PartialSwap if != surface size.
+  // |content_bounds| = content area for SwapWithBounds if non-empty; rectangles
+  // may overlap. If neither is provided, use standard swap. Providing both
+  // |sub_buffer_rect| and |content_bounds| is not supported.

[danakj, 2017/02/16 18:54:19]

I think this is a little misleading. sub_buffer_rect is always provided. But it
may be == surface size. It may also be empty even if not using partial swap but
there's no damage (after doing overlays? when the context supports empty swaps)

That said.. comparing rects are == is a little uh.. oldschool? Maybe this is a
good case for an Optional sub_buffer_rect. That'd make intentions more explicit.
If you agree we could do that as a separate CL for this one to build on.

[halliwell, 2017/02/17 14:08:45]

Yep, looked at this a little closer:
* Optional does sound clearer vs comparing rects.  I'll try putting together a
CL for that first.
* I think this comment is still true to the extent that content_bounds and
sub_buffer_rect can't both be provided.  But yes, there is an additional case -
sub_buffer_rect isn't just for PartialSwap, it can also be empty in the case
where CommitOverlayPlanes is used.  I'll rephrase to clarify in next patchset.

[halliwell, 2017/02/23 18:01:46]

Ok, comment updated, and using Optional now.

   gfx::Rect sub_buffer_rect;
+  std::vector<gfx::Rect> content_bounds;
   std::vector<ui::LatencyInfo> latency_info;
 
  private: