chromeos: only hold pointer events if SurfaceId actually changes

BUG=929914
TEST=none

Change-Id: I9174b13bd634ac2e69e5478e5acfe91262c9679a
Reviewed-on: https://chromium-review.googlesource.com/c/1475938
Commit-Queue: Scott Violet <sky@chromium.org>
Commit-Queue: Saman Sami <samans@chromium.org>
Auto-Submit: Scott Violet <sky@chromium.org>
Reviewed-by: Saman Sami <samans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632837}

services/ws/client_root.cc

@@ -244,11 +244,13 @@ void ClientRoot::UpdateLocalSurfaceIdAndClientSurfaceEmbedder() {
   const viz::SurfaceId surface_id(
       window_->GetFrameSinkId(),
       proxy_window->local_surface_id_allocation()->local_surface_id());
+  const bool surface_id_changed =
+      surface_id != client_surface_embedder_->GetSurfaceId();
   client_surface_embedder_->SetSurfaceId(surface_id);
 
   // This triggers holding events until the frame has been activated. This
   // ensures smooth resizes.
-  if (ShouldAssignLocalSurfaceId() && window_->GetHost())
+  if (surface_id_changed && ShouldAssignLocalSurfaceId() && window_->GetHost())
     window_->GetHost()->compositor()->OnChildResizing();
 }