DesktopAura: Track windows "owned" via the DesktopWindowTreeHost

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 12d11166f2452f579f464c2aa520cc1357488595..6684dc8e07e26734f220dcf8b663a0f82e1aad2e 100644
--- a/ui/views/mus/desktop_window_tree_host_mus.cc
+++ b/ui/views/mus/desktop_window_tree_host_mus.cc
@@ -667,6 +667,12 @@ bool DesktopWindowTreeHostMus::ShouldUseDesktopNativeCursorManager() const {
   return false;
 }
 
+std::vector<DesktopWindowTreeHost*>
+DesktopWindowTreeHostMus::GetOwnedTopLevelHosts() const {
+  return std::vector<DesktopWindowTreeHost*>(children_.begin(),
+                                             children_.end());
+}
+
 void DesktopWindowTreeHostMus::OnWindowManagerFrameValuesChanged() {
   NonClientView* non_client_view =
       native_widget_delegate_->AsWidget()->non_client_view();