Fix a crash with weston-terminal

With weston-terminal, exo can submit a frame before resizing bounds
of a shell surface. In that case, the local surface id is not set to
the frame sink for mus. It causes the crash. Fixing the crash by
setting the local surface id to the frame sink during creating the
frame sink.

Bug: None
Change-Id: I5b3202c176d2788a52aedbb259e7b18b5f5b8dd4
Reviewed-on: https://chromium-review.googlesource.com/682768Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Peng Huang <penghuang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504193}

ui/aura/mus/window_port_mus.cc

@@ -549,8 +549,9 @@ WindowPortMus::CreateLayerTreeFrameSink() {
   auto frame_sink = RequestLayerTreeFrameSink(
       nullptr,
       aura::Env::GetInstance()->context_factory()->GetGpuMemoryBufferManager());
-  local_layer_tree_frame_sink_ = frame_sink->GetWeakPtr();
   local_surface_id_ = local_surface_id_allocator_.GenerateId();
+  frame_sink->SetLocalSurfaceId(local_surface_id_);
+  local_layer_tree_frame_sink_ = frame_sink->GetWeakPtr();
   return std::move(frame_sink);
 }