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 ab5dbabef5ec613aaf95798a000b1ac3d5bb667a..1f2f85eded6fca577016a0aca2fbcc4387360149 100644
--- a/ui/aura/mus/window_port_mus.cc
+++ b/ui/aura/mus/window_port_mus.cc
@@ -231,10 +231,17 @@ void WindowPortMus::ReorderFromServer(WindowMus* child,
     window_->StackChildAbove(child->GetWindow(), relative->GetWindow());
 }
 
-void WindowPortMus::SetBoundsFromServer(const gfx::Rect& bounds) {
+void WindowPortMus::SetBoundsFromServer(
+    const gfx::Rect& bounds,
+    const base::Optional<cc::LocalSurfaceId>& local_surface_id) {
   ServerChangeData data;
   data.bounds_in_dip = bounds;
   ScopedServerChange change(this, ServerChangeType::BOUNDS, data);
+  last_surface_size_ = bounds.size();
+  if (local_surface_id)
+    local_surface_id_ = *local_surface_id;
+  else
+    local_surface_id_ = cc::LocalSurfaceId();
   window_->SetBounds(bounds);
 }
 
@@ -284,6 +291,22 @@ void WindowPortMus::SetFrameSinkIdFromServer(
   // then we are ready to embed.
 }
 
+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()) {
@@ -363,6 +386,10 @@ WindowPortMus::ChangeSource WindowPortMus::OnTransientChildRemoved(
              : ChangeSource::LOCAL;
 }
 
+const cc::LocalSurfaceId& WindowPortMus::GetLocalSurfaceId() {
+  return local_surface_id_;
+}
+
 std::unique_ptr<WindowMusChangeData>
 WindowPortMus::PrepareForServerBoundsChange(const gfx::Rect& bounds) {
   std::unique_ptr<WindowMusChangeDataImpl> data(