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

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

Index: third_party/WebKit/Source/core/input/EventHandler.cpp
diff --git a/third_party/WebKit/Source/core/input/EventHandler.cpp b/third_party/WebKit/Source/core/input/EventHandler.cpp
index 9650421690c6b997d82c351d627217e073780bd6..bb4e6b8bc2434d80589a0622c233c6a5ee0339bf 100644
--- a/third_party/WebKit/Source/core/input/EventHandler.cpp
+++ b/third_party/WebKit/Source/core/input/EventHandler.cpp
@@ -1339,6 +1339,8 @@ WebInputEventResult EventHandler::handleGestureEvent(
 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());
@@ -1370,12 +1372,17 @@ WebInputEventResult EventHandler::handleGestureEventInFrame(
 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);
 }