bindings: Add empty checks for toV8()

Source/bindings/core/v8/V8ErrorHandler.cpp

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 31 matching lines @@
 
 namespace blink {
 
 V8ErrorHandler::V8ErrorHandler(v8::Local<v8::Object> listener, bool isInline, ScriptState* scriptState)
     : V8EventListener(listener, isInline, scriptState)
 {
 }
 
 v8::Local<v8::Value> V8ErrorHandler::callListenerFunction(ScriptState* scriptState, v8::Local<v8::Value> jsEvent, Event* event)
 {
+    ASSERT(!jsEvent.IsEmpty());
     if (!event->hasInterface(EventNames::ErrorEvent))
         return V8EventListener::callListenerFunction(scriptState, jsEvent, event);
 
     ErrorEvent* errorEvent = static_cast<ErrorEvent*>(event);
     if (errorEvent->world() && errorEvent->world() != &world())
         return v8::Null(isolate());
 
     v8::Local<v8::Object> listener = getListenerObject(scriptState->executionContext());
     if (listener.IsEmpty() || !listener->IsFunction())
         return v8::Null(isolate());
@@ skipping 33 matching lines @@
         V8HiddenValue::setHiddenValue(isolate, v8::Local<v8::Object>::Cast(wrappedEvent), V8HiddenValue::error(isolate), data);
     }
 }
 
 bool V8ErrorHandler::shouldPreventDefault(v8::Local<v8::Value> returnValue)
 {
     return returnValue->IsBoolean() && returnValue.As<v8::Boolean>()->Value();
 }
 
 } // namespace blink