WIP - Gutterless resize on Windows

ui/compositor/compositor.h

Index: ui/compositor/compositor.h
diff --git a/ui/compositor/compositor.h b/ui/compositor/compositor.h
index 1602d30caae8b7b4ad72f727422e309428722004..eacf804a77161b09810b2dd3783d009aa598e192 100644
--- a/ui/compositor/compositor.h
+++ b/ui/compositor/compositor.h
@@ -324,9 +324,12 @@ class COMPOSITOR_EXPORT Compositor
     return surface_id_allocator_.get();
   }
 
+  gfx::Size last_swapped_frame_size() const { return last_swapped_frame_size_; }
+
  private:
   friend class base::RefCounted<Compositor>;
   friend class CompositorLock;
+  class ResizeSwapPromise;
 
   // Called by CompositorLock.
   void UnlockCompositor();
@@ -334,6 +337,16 @@ class COMPOSITOR_EXPORT Compositor
   // Called to release any pending CompositorLock
   void CancelCompositorLock();
 
+  void set_pending_swapped_frame_size(
+      const gfx::Size& pending_swapped_frame_size) {
+    pending_swapped_frame_size_ = pending_swapped_frame_size;
+  }
+
+  void UpdateLastSwappedFrameSize() {
+    last_swapped_frame_size_ = pending_swapped_frame_size_;
+    pending_swapped_frame_size_ = gfx::Size();
+  }
+
   gfx::Size size_;
 
   ui::ContextFactory* context_factory_;
@@ -372,6 +385,14 @@ class COMPOSITOR_EXPORT Compositor
   // Used to send to any new CompositorBeginFrameObserver immediately.
   cc::BeginFrameArgs missed_begin_frame_args_;
 
+  // Used to track the last swapped frame size. We use a swap promise to track
+  // the progression of a frame through resizing of the compositor to posting
+  // swap buffers. Once posted, the frame's size is recorded to
+  // |pending_swapped_frame_size_|. Once a swap completes, the pending size is
+  // promoted to the |last_swapped_frame_size_|.
+  gfx::Size last_swapped_frame_size_;
+  gfx::Size pending_swapped_frame_size_;
+
   base::WeakPtrFactory<Compositor> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Compositor);