Tab dragging as implemented as a mus API.

services/ui/public/interfaces/window_tree.mojom

Index: services/ui/public/interfaces/window_tree.mojom
diff --git a/services/ui/public/interfaces/window_tree.mojom b/services/ui/public/interfaces/window_tree.mojom
index ed7175b3296bca4a065a552503f54b0a8443f465..a15f7bf5c7117e6b21cc6037a3bb34d943b92fab 100644
--- a/services/ui/public/interfaces/window_tree.mojom
+++ b/services/ui/public/interfaces/window_tree.mojom
@@ -233,6 +233,17 @@ interface WindowTree {
   // single Atomic32, which represent the current location of the mouse cursor
   // where the location is (x << 16) | y.
   GetCursorLocationMemory() => (handle<shared_buffer> cursor_buffer);
+
+  // Tells the window manager to start moving the window. OnChangeCompleted is
+  // called on whether the move was canceled. Because there's a delay between
+  // when a client sends this message and when the window manager starts acting
+  // on it, pass the cursor location at the start of the move.
+  PerformWindowMove(uint32 change_id, uint32 window_id, MoveLoopSource source,
+                    gfx.mojom.Point cursor);
+
+  // Tells the window manager to cancel any in progress window move started with
+  // StartWindowMove() and to revert the window bounds to how they were.
+  CancelWindowMove(uint32 window_id);
 };
 
 // Changes to windows are not sent to the connection that originated the