aura-mus: add a drag representation image.

services/ui/ws/drag_controller.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "services/ui/ws/drag_controller.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "services/ui/public/interfaces/cursor.mojom.h"
@@ skipping 89 matching lines @@
   while (current_target && !current_target->can_accept_drops())
     current_target = current_target->parent();
 
   if (current_target) {
     // If we're non-null, we're about to use |current_target| in some
     // way. Ensure that we receive notifications that this window has gone
     // away.
     EnsureWindowObserved(current_target);
   }
 
+  source_->OnDragContinued(screen_position);
+
   if (current_target && current_target == current_target_window_ &&
       event.type() != ET_POINTER_UP) {
     QueueOperation(current_target, OperationType::OVER, event_flags,
                    screen_position);
   } else if (current_target != current_target_window_) {
     if (current_target_window_) {
       QueueOperation(current_target_window_, OperationType::LEAVE, event_flags,
                      screen_position);
     }
 
@@ skipping 236 matching lines @@
       return "LEAVE";
     case OperationType::DROP:
       return "DROP";
   }
   NOTREACHED();
   return std::string();
 }
 
 }  // namespace ws
 }  // namespace ui