mus: Use the new drag API to implement tab dragging in chrome.

ui/views/mus/native_widget_mus.h

Index: ui/views/mus/native_widget_mus.h
diff --git a/ui/views/mus/native_widget_mus.h b/ui/views/mus/native_widget_mus.h
index 33da5378358e1cc3cbb3d1b975ea63e7f065474c..1af85925092e317e8dfcdba66f56a9f04e859148 100644
--- a/ui/views/mus/native_widget_mus.h
+++ b/ui/views/mus/native_widget_mus.h
@@ -220,6 +220,9 @@ class VIEWS_MUS_EXPORT NativeWidgetMus
   void OnGestureEvent(ui::GestureEvent* event) override;
 
   // Overridden from aura::WindowTreeHostObserver:
+  void OnHostResized(const aura::WindowTreeHost* host) override;
+  void OnHostMoved(const aura::WindowTreeHost* host,
+                   const gfx::Point& new_origin) override;
   void OnHostCloseRequested(const aura::WindowTreeHost* host) override;
 
   // Overridden from mus::InputEventHandler:
@@ -264,6 +267,11 @@ private:
   // a separate class.
   std::unique_ptr<MusWindowObserver> mus_window_observer_;
 
+  // This is misnamed; The native widget interface offers something called
+  // "native window properties" which are properties which it stores locally,
+  // and this is used to unsafely pass void* pointers around chrome.
+  std::map<std::string, void*> native_window_properties_;
+
   // Aura configuration.
   std::unique_ptr<SurfaceContextFactory> context_factory_;
   std::unique_ptr<WindowTreeHostMus> window_tree_host_;