views/win: Re-enable Display swap without touching cc.

Reset the size of the viz::Display directly to the original size, instead
of triggering a size-change in the layer-compositor (cc) too, when a resize
operation ends without actually resizing the window on Windows.

BUG=821987

Change-Id: I97c6e76fd52b46d782a172fc54bb7cf9a0e0a1d6
Reviewed-on: https://chromium-review.googlesource.com/1006518Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550031}

ui/compositor/compositor.cc

@@ -336,9 +336,15 @@ void Compositor::ScheduleRedrawRect(const gfx::Rect& damage_rect) {
 }
 
 void Compositor::DisableSwapUntilResize() {
+  DCHECK(context_factory_private_);
   context_factory_private_->ResizeDisplay(this, gfx::Size());
 }
 
+void Compositor::ReenableSwap() {
+  DCHECK(context_factory_private_);
+  context_factory_private_->ResizeDisplay(this, size_);
+}
+
 void Compositor::SetLatencyInfo(const ui::LatencyInfo& latency_info) {
   std::unique_ptr<cc::SwapPromise> swap_promise(
       new cc::LatencyInfoSwapPromise(latency_info));

ui/compositor/compositor.h

@@ -260,6 +260,7 @@ class COMPOSITOR_EXPORT Compositor : public cc::LayerTreeHostClient,
   // Finishes all outstanding rendering and disables swapping on this surface
   // until it is resized.
   void DisableSwapUntilResize();
+  void ReenableSwap();
 
   void SetLatencyInfo(const LatencyInfo& latency_info);
 

ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc

@@ -969,13 +969,8 @@ void DesktopWindowTreeHostWin::HandleWindowSizeUnchanged() {
   // changed (can occur on Windows 10 when snapping a window to the side of
   // the screen). In that case do a resize to the current size to reenable
   // swaps.
-  // TODO(ccameron): This will violate surface invariants.
-  if (compositor()) {
-    compositor()->SetScaleAndSize(
-        compositor()->device_scale_factor(),
-        message_handler_->GetClientAreaBounds().size(),
-        window()->GetLocalSurfaceId());
-  }
+  if (compositor())
+    compositor()->ReenableSwap();
 }
 
 void DesktopWindowTreeHostWin::HandleWindowScaleFactorChanged(