Aura-Mus: Allocate a LocalSurfaceId on size change

ui/aura/mus/window_port_mus.cc

Index: ui/aura/mus/window_port_mus.cc
diff --git a/ui/aura/mus/window_port_mus.cc b/ui/aura/mus/window_port_mus.cc
index 1ad03c8900ca322f41f9a2f32b1493dea0c1f3bd..1da946e3a821bebf666674f4b8556dbb31103f98 100644
--- a/ui/aura/mus/window_port_mus.cc
+++ b/ui/aura/mus/window_port_mus.cc
@@ -283,6 +283,26 @@ void WindowPortMus::SetFrameSinkIdFromServer(
   // then we are ready to embed.
 }
 
+const cc::LocalSurfaceId& WindowPortMus::GetLocalSurfaceId() {
+  return local_surface_id_;
+}
+
+const cc::LocalSurfaceId& WindowPortMus::GetOrAllocateLocalSurfaceId(
+    const gfx::Size& surface_size) {
+  if (last_surface_size_ == surface_size && local_surface_id_.is_valid())
+    return local_surface_id_;
+
+  local_surface_id_ = local_surface_id_allocator_.GenerateId();
+  last_surface_size_ = surface_size;
+
+  // TODO(fsamuel): If surface synchronization is enabled and the FrameSinkId
+  // is available, then immediately embed the SurfaceId. The newly generated
+  // frame by the embedder will block in the display compositor until the
+  // child submits a corresponding CompositorFrame or a deadline hits.
+
+  return local_surface_id_;
+}
+
 void WindowPortMus::SetSurfaceInfoFromServer(
     const cc::SurfaceInfo& surface_info) {
   if (surface_info_.is_valid()) {