Tab dragging as implemented as a mus API.

components/mus/demo/mus_demo.h

Index: components/mus/demo/mus_demo.h
diff --git a/components/mus/demo/mus_demo.h b/components/mus/demo/mus_demo.h
index dbb62647294e2606b0ce671fcf4c050a5fc32f22..a8406b6659aecfb096aa93f235b88ef410fca665 100644
--- a/components/mus/demo/mus_demo.h
+++ b/components/mus/demo/mus_demo.h
@@ -60,6 +60,10 @@ class MusDemo : public shell::ShellClient,
   void OnWmNewDisplay(mus::Window* window,
                       const display::Display& display) override;
   void OnAccelerator(uint32_t id, const ui::Event& event) override;
+  void OnWmPerformMoveLoop(uint32_t change_id,
+                           uint32_t window_id,
+                           const gfx::Point& cursor_location) override;
+  void OnWmCancelMoveLoop(uint32_t window_id) override;
 
   // Allocate a bitmap the same size as the window to draw into.
   void AllocBitmap();