Converts chrome to aura-mus

ui/views/mus/desktop_window_tree_host_mus.cc

Index: ui/views/mus/desktop_window_tree_host_mus.cc
diff --git a/ui/views/mus/desktop_window_tree_host_mus.cc b/ui/views/mus/desktop_window_tree_host_mus.cc
index 12c9e7fd24c77fe6970f50b2b14516c6849938a4..c3097bd499666b4fe677a99dc499a001b7568652 100644
--- a/ui/views/mus/desktop_window_tree_host_mus.cc
+++ b/ui/views/mus/desktop_window_tree_host_mus.cc
@@ -180,6 +180,11 @@ DesktopWindowTreeHostMus::DesktopWindowTreeHostMus(
       close_widget_factory_(this) {
   aura::Env::GetInstance()->AddObserver(this);
   MusClient::Get()->AddObserver(this);
+  // DesktopNativeWidgetAura registers the association between |content_window_|
+  // and Widget, but code may also want to go from the root (window()) to the
+  // Widget. This call enables that.
+  NativeWidgetAura::RegisterNativeWidgetForWindow(desktop_native_widget_aura,
+                                                  window());
   // TODO: use display id and bounds if available, likely need to pass in
   // InitParams for that.
 }