Tab dragging as implemented as a mus API.

components/mus/public/interfaces/window_manager.mojom

Index: components/mus/public/interfaces/window_manager.mojom
diff --git a/components/mus/public/interfaces/window_manager.mojom b/components/mus/public/interfaces/window_manager.mojom
index ed0ffe172a1023bdfbbf6e7dd0af7c276247af1f..9e4730bfb102632182e44dd604464a5d2a2aff3a 100644
--- a/components/mus/public/interfaces/window_manager.mojom
+++ b/components/mus/public/interfaces/window_manager.mojom
@@ -83,6 +83,15 @@ interface WindowManager {
   // can update the UI for the janky windows.
   WmClientJankinessChanged(uint16 client_id, bool janky);
 
+  // Asks the WindowManager to interactively move the window. This will return
+  // whether this completed successfully or not through the client's
+  // OnWmMoveLoopCompleted().
+  WmPerformMoveLoop(uint32 change_id, uint32 window_id,

[sky, 2016/06/22 23:47:56]

nit: window_id on its own line.
Also, document what cursor_location is as it isn't obvious from reading the
description.

+                    gfx.mojom.Point cursor_location);
+
+  // Asks the WindowManager to cancel any outstanding move loop on |window_id|.
+  WmCancelMoveLoop(uint32 window_id);
+
   // An accelerator registered via AddAccelerator() has been triggered.
   OnAccelerator(uint32 id, ui.mojom.Event event);
 };
@@ -131,4 +140,8 @@ interface WindowManagerClient {
   // Response from WmCreateTopLevelWindow() informing the client of the id for
   // the new window.
   OnWmCreatedTopLevelWindow(uint32 change_id, uint32 window_id);
+
+  // Response from WmPerformMoveLoop(). Returns true if the move loop was
+  // completed successfully.
+  OnWmMoveLoopCompleted(uint32 change_id, uint32 window_id, bool completed);

[sky, 2016/06/22 23:47:56]

Why do you need to supply the window_id here as well? mus should know the window
based on the change_id.

 };