Getting rid of SurfaceIdHandler as it is no longer needed.

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 da1ae155fc2cc98e5f27764f39a5c79bde01a128..abc2c23047975da0d8c507c4f298f878f0b78100 100644
--- a/ui/aura/mus/window_port_mus.cc
+++ b/ui/aura/mus/window_port_mus.cc
@@ -9,7 +9,6 @@
 #include "ui/aura/client/transient_window_client.h"
 #include "ui/aura/mus/client_surface_embedder.h"
 #include "ui/aura/mus/property_converter.h"
-#include "ui/aura/mus/surface_id_handler.h"
 #include "ui/aura/mus/window_tree_client.h"
 #include "ui/aura/mus/window_tree_client_delegate.h"
 #include "ui/aura/window.h"
@@ -255,12 +254,6 @@ void WindowPortMus::SetSurfaceInfoFromServer(
       // TODO(kylechar): Start return reference here?
     }
   }
-  WindowPortMus* parent = Get(window_->parent());
-  // TODO(mfomitchev): This is unused. We probably don't need this.
-  if (parent && parent->surface_id_handler_) {
-    parent->surface_id_handler_->OnChildWindowSurfaceChanged(window_,
-                                                             surface_info);
-  }
 
   // The fact that SetSurfaceIdFromServer was called means that this window
   // corresponds to an embedded client.