Tab dragging as implemented as a mus API.

components/mus/public/interfaces/window_manager_constants.mojom

Index: components/mus/public/interfaces/window_manager_constants.mojom
diff --git a/components/mus/public/interfaces/window_manager_constants.mojom b/components/mus/public/interfaces/window_manager_constants.mojom
index acdf16b4478ad66d072f8e7a032d93cd1dab2c92..a732de6ff209889340e1a1a82aecfb5495bcac65 100644
--- a/components/mus/public/interfaces/window_manager_constants.mojom
+++ b/components/mus/public/interfaces/window_manager_constants.mojom
@@ -62,6 +62,13 @@ struct Display {
   FrameDecorationValues frame_decoration_values;
 };
 
+// Whether a client initiated move loop was started with a mouse event or a
+// touch event.
+enum MoveLoopSource {
+  MOUSE,
+  TOUCH
+};
+
 enum WindowType {
   // These constants come from Widget::InitParams. See it for details.
   // TODO: see if we can reduce this set. For example, why do we need both