Tab dragging as implemented as a mus API.

ash/mus/window_manager.h

Index: ash/mus/window_manager.h
diff --git a/ash/mus/window_manager.h b/ash/mus/window_manager.h
index a922d52291fa3523b9e3c1041c509c474d475690..686d2bc77dc30601aef66201c51a93645005ac70 100644
--- a/ash/mus/window_manager.h
+++ b/ash/mus/window_manager.h
@@ -104,6 +104,11 @@ class WindowManager : public ::mus::WindowManagerDelegate,
   void OnWmNewDisplay(::mus::Window* window,
                       const display::Display& display) override;
   void OnAccelerator(uint32_t id, const ui::Event& event) override;
+  void OnWmPerformMoveLoop(::mus::Window* window,
+                           ::mus::mojom::MoveLoopSource source,
+                           const gfx::Point& cursor_location,
+                           const base::Callback<void(bool)>& on_done) override;
+  void OnWmCancelMoveLoop(::mus::Window* window) override;
 
   // TODO(sky): this is unfortunate, remove.
   WindowManagerApplication* window_manager_app_;