Fix an interactive ui test

ui/aura/window_event_dispatcher.cc

 // Copyright 2014 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 "ui/aura/window_event_dispatcher.h"
 
 #include <stddef.h>
 
 #include "base/bind.h"
 #include "base/logging.h"
@@ skipping 296 matching lines @@
   // If a window has been hidden between the touch event and now, the associated
   // gestures may not have a valid target.
   if (!target)
     return details;
 
   for (const auto& event : gestures) {
     event->ConvertLocationToTarget(window(), target);
     details = DispatchEvent(target, event.get());
     if (details.dispatcher_destroyed || details.target_destroyed)
       break;
+    // If the target window has moved off to a different WindowTreeHost, then
+    // abort processing the rest of the events.
+    if (!window()->Contains(target))
+      break;
   }
   return details;
 }
 
 void WindowEventDispatcher::OnWindowHidden(Window* invisible,
                                            WindowHiddenReason reason) {
   // If the window the mouse was pressed in becomes invisible, it should no
   // longer receive mouse events.
   if (invisible->Contains(mouse_pressed_handler_))
     mouse_pressed_handler_ = NULL;
@@ skipping 594 matching lines @@
   }
 
   // This flag is set depending on the gestures recognized in the call above,
   // and needs to propagate with the forwarded event.
   event->set_may_cause_scrolling(orig_event.may_cause_scrolling());
 
   return PreDispatchLocatedEvent(target, event);
 }
 
 }  // namespace aura