mash: Relay some Chrome aura window properties to Ash.

ui/views/mus/mus_client.cc

Index: ui/views/mus/mus_client.cc
diff --git a/ui/views/mus/mus_client.cc b/ui/views/mus/mus_client.cc
index 2a73231972a333202e7dd245ed9ec78d49577652..7f5235b1fe8f31dc98f83602883a90a6d7dc5bbd 100644
--- a/ui/views/mus/mus_client.cc
+++ b/ui/views/mus/mus_client.cc
@@ -226,6 +226,11 @@ void MusClient::RemoveObserver(MusClientObserver* observer) {
   observer_list_.RemoveObserver(observer);
 }
 
+void MusClient::OnWindowPropertyChanged(aura::Window* window, const void* key) {
+  for (auto& observer : observer_list_)
+    observer.OnWindowPropertyChanged(window, key);
+}
+
 void MusClient::OnEmbed(
     std::unique_ptr<aura::WindowTreeHostMus> window_tree_host) {
   NOTREACHED();