Wires up transient windows for aura-mus

ui/aura/mus/window_tree_client.h

Index: ui/aura/mus/window_tree_client.h
diff --git a/ui/aura/mus/window_tree_client.h b/ui/aura/mus/window_tree_client.h
index f5d74b2aba52a5d90a6e76f0d59b94668842fcd8..ee717813ab1b846036259e08cc6246153b382b4e 100644
--- a/ui/aura/mus/window_tree_client.h
+++ b/ui/aura/mus/window_tree_client.h
@@ -24,6 +24,7 @@
 #include "ui/aura/aura_export.h"
 #include "ui/aura/client/capture_client_observer.h"
 #include "ui/aura/client/focus_change_observer.h"
+#include "ui/aura/client/transient_window_client_observer.h"
 #include "ui/aura/mus/mus_types.h"
 #include "ui/aura/mus/window_manager_delegate.h"
 #include "ui/aura/mus/window_tree_host_mus_delegate.h"
@@ -74,9 +75,10 @@ class AURA_EXPORT WindowTreeClient
     : NON_EXPORTED_BASE(public ui::mojom::WindowTreeClient),
       NON_EXPORTED_BASE(public ui::mojom::WindowManager),
       public WindowManagerClient,
+      public WindowTreeHostMusDelegate,
       public client::CaptureClientObserver,
       public client::FocusChangeObserver,
-      public WindowTreeHostMusDelegate {
+      public client::TransientWindowClientObserver {
  public:
   explicit WindowTreeClient(
       WindowTreeClientDelegate* delegate,
@@ -441,6 +443,12 @@ class AURA_EXPORT WindowTreeClient
   // Overriden from WindowTreeHostMusDelegate:
   void SetRootWindowBounds(Window* window, gfx::Rect* bounds) override;
 
+  // Override from client::TransientWindowClientObserver:
+  void OnTransientChildWindowAdded(Window* parent,
+                                   Window* transient_child) override;
+  void OnTransientChildWindowRemoved(Window* parent,
+                                     Window* transient_child) override;
+
   // The one int in |cursor_location_mapping_|. When we read from this
   // location, we must always read from it atomically.
   base::subtle::Atomic32* cursor_location_memory() {