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 9ea8b45f855bdb375a51dd4d92ba78e3cbd091d4..1ab50466089212065f1d7b66b624024f302270c4 100644
--- a/ash/mus/window_manager.h
+++ b/ash/mus/window_manager.h
@@ -101,6 +101,11 @@ class WindowManager : public ::ui::WindowManagerDelegate,
   void OnWmNewDisplay(::ui::Window* window,
                       const display::Display& display) override;
   void OnAccelerator(uint32_t id, const ui::Event& event) override;
+  void OnWmPerformMoveLoop(::ui::Window* window,
+                           ::ui::mojom::MoveLoopSource source,
+                           const gfx::Point& cursor_location,
+                           const base::Callback<void(bool)>& on_done) override;
+  void OnWmCancelMoveLoop(::ui::Window* window) override;
 
   shell::Connector* connector_;