Fix detached event listener attribute updating.

third_party/WebKit/Source/bindings/core/v8/V8AbstractEventListener.cpp

Index: third_party/WebKit/Source/bindings/core/v8/V8AbstractEventListener.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/V8AbstractEventListener.cpp b/third_party/WebKit/Source/bindings/core/v8/V8AbstractEventListener.cpp
index f37c4371737d9f5b7e06eff8289acb743fc36895..3354ab4efb88707c25e5d7e0994ff1241925236b 100644
--- a/third_party/WebKit/Source/bindings/core/v8/V8AbstractEventListener.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/V8AbstractEventListener.cpp
@@ -204,7 +204,8 @@ bool V8AbstractEventListener::BelongsToTheCurrentWorld(
     return true;
   // If currently parsing, the parser could be accessing this listener
   // outside of any v8 context; check if it belongs to the main world.
-  if (!GetIsolate()->InContext() && execution_context->IsDocument()) {
+  if (!GetIsolate()->InContext() && execution_context &&
+      execution_context->IsDocument()) {
     Document* document = ToDocument(execution_context);
     if (document->Parser() && document->Parser()->IsParsing())
       return World().IsMainWorld();