Add assert to catch dispatching events over dying targets.

third_party/WebKit/Source/core/events/EventTarget.cpp

Index: third_party/WebKit/Source/core/events/EventTarget.cpp
diff --git a/third_party/WebKit/Source/core/events/EventTarget.cpp b/third_party/WebKit/Source/core/events/EventTarget.cpp
index 15bd846035344ffc91e74802d52da4c5e6adea18..f0c63db706f3aec9ce49d35d6f09605bd361ec67 100644
--- a/third_party/WebKit/Source/core/events/EventTarget.cpp
+++ b/third_party/WebKit/Source/core/events/EventTarget.cpp
@@ -275,6 +275,13 @@ bool EventTarget::dispatchEvent(PassRefPtrWillBeRawPtr<Event> event)
 
 bool EventTarget::dispatchEventInternal(PassRefPtrWillBeRawPtr<Event> event)
 {
+#if ENABLE(OILPAN)
+    // Dispatching events for a target that is about to be swept,
+    // is unsafe and not allowed. If this assert triggers, your
+    // EventTarget needs to extend its lifetime accordingly.
+    // Using mechanisms like e.g., ActiveDOMObject::hasPendingActivity().
+    ASSERT(!Heap::willObjectBeLazilySwept(this));
+#endif
     event->setTarget(this);
     event->setCurrentTarget(this);
     event->setEventPhase(Event::AT_TARGET);