Don't enter gesture event handling when a frame is detached.

third_party/WebKit/Source/core/input/EventHandler.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights
  * reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2012 Digia Plc. and/or its subsidiary(-ies)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
@@ skipping 1321 matching lines @@
   // event type.
   GestureEventWithHitTestResults targetedEvent =
       targetGestureEvent(gestureEvent);
 
   return handleGestureEvent(targetedEvent);
 }
 
 WebInputEventResult EventHandler::handleGestureEvent(
     const GestureEventWithHitTestResults& targetedEvent) {
   TRACE_EVENT0("input", "EventHandler::handleGestureEvent");
+  if (!m_frame->host())
+    return WebInputEventResult::NotHandled;
 
   // Propagation to inner frames is handled below this function.
   ASSERT(m_frame == m_frame->localFrameRoot());
 
   // Non-scrolling related gesture events do a single cross-frame hit-test and
   // jump directly to the inner most frame. This matches handleMousePressEvent
   // etc.
   ASSERT(!targetedEvent.event().isScrollEvent());
 
   // Update mouseout/leave/over/enter events before jumping directly to the
@@ skipping 11 matching lines @@
 }
 
 WebInputEventResult EventHandler::handleGestureEventInFrame(
     const GestureEventWithHitTestResults& targetedEvent) {
   return m_gestureManager->handleGestureEventInFrame(targetedEvent);
 }
 
 WebInputEventResult EventHandler::handleGestureScrollEvent(
     const PlatformGestureEvent& gestureEvent) {
   TRACE_EVENT0("input", "EventHandler::handleGestureScrollEvent");
+  if (!m_frame->host())
+    return WebInputEventResult::NotHandled;
 
   return m_scrollManager->handleGestureScrollEvent(gestureEvent);
 }
 
 WebInputEventResult EventHandler::handleGestureScrollEnd(
     const PlatformGestureEvent& gestureEvent) {
+  if (!m_frame->host())
+    return WebInputEventResult::NotHandled;
+
   return m_scrollManager->handleGestureScrollEnd(gestureEvent);
 }
 
 void EventHandler::setMouseDownMayStartAutoscroll() {
   m_mouseEventManager->setMouseDownMayStartAutoscroll();
 }
 
 bool EventHandler::isScrollbarHandlingGestures() const {
   return m_scrollManager->isScrollbarHandlingGestures();
 }
@@ skipping 711 matching lines @@
 }
 
 FrameHost* EventHandler::frameHost() const {
   if (!m_frame->page())
     return nullptr;
 
   return &m_frame->page()->frameHost();
 }
 
 }  // namespace blink