Treat non-callable input as null for EventHandler attributes

Source/bindings/v8/V8EventListener.cpp

Index: Source/bindings/v8/V8EventListener.cpp
diff --git a/Source/bindings/v8/V8EventListener.cpp b/Source/bindings/v8/V8EventListener.cpp
index 8ada755b27a3e233f0a5002bafcd30e3ec8f75f2..9a0751f2ae6b993065d9904420340aeebdd1ea90 100644
--- a/Source/bindings/v8/V8EventListener.cpp
+++ b/Source/bindings/v8/V8EventListener.cpp
@@ -55,6 +55,8 @@ v8::Local<v8::Function> V8EventListener::getListenerFunction(ScriptExecutionCont
         return v8::Local<v8::Function>::Cast(listener);
 
     if (listener->IsObject()) {
+        // EventHandler attributes should only accept JS Functions as input.
+        ASSERT(!isAttribute());

[arv (Not doing code reviews), 2013/08/08 14:41:28]

Maybe use ASSERT_WITH_MESSAGE?

         v8::Local<v8::Value> property = listener->Get(v8::String::NewSymbol("handleEvent"));
         // Check that no exceptions were thrown when getting the
         // handleEvent property and that the value is a function.