Tab dragging as implemented as a mus API.

components/mus/test_wm/test_wm.cc

Index: components/mus/test_wm/test_wm.cc
diff --git a/components/mus/test_wm/test_wm.cc b/components/mus/test_wm/test_wm.cc
index 39ad375983987d37d4a157cc241854b96f6018fa..f7fdca49f3657dd419a21528727dcae816cb8084 100644
--- a/components/mus/test_wm/test_wm.cc
+++ b/components/mus/test_wm/test_wm.cc
@@ -89,6 +89,12 @@ class TestWM : public shell::ShellClient,
   void OnAccelerator(uint32_t id, const ui::Event& event) override {
     // Don't care.
   }
+  void OnWmPerformMoveLoop(uint32_t change_id,
+                           uint32_t window_id,
+                           const gfx::Point& cursor_location) override {
+    // Don't care.
+  }
+  void OnWmCancelMoveLoop(uint32_t window_id) override {}
 
   mus::Window* root_ = nullptr;
   mus::WindowManagerClient* window_manager_client_ = nullptr;