toImplArguments should return HeapVector for Union types.

Source/bindings/templates/methods.cpp

Index: Source/bindings/templates/methods.cpp
diff --git a/Source/bindings/templates/methods.cpp b/Source/bindings/templates/methods.cpp
index 50c344af3ab500a04f7a3b067982e12718fdeff7..1ddbe29750b3f7a7ce6d4b4b1740a210e95dd699 100644
--- a/Source/bindings/templates/methods.cpp
+++ b/Source/bindings/templates/methods.cpp
@@ -466,7 +466,7 @@ static void {{method.name}}MethodCallback{{world_suffix}}(const v8::FunctionCall
     if (contextData && contextData->activityLogger()) {
     {% endif %}
         ExceptionState exceptionState(ExceptionState::ExecutionContext, "{{method.name}}", "{{interface_name}}", info.Holder(), info.GetIsolate());
-        Vector<v8::Local<v8::Value>> loggerArgs = toImplArguments<v8::Local<v8::Value>>(info, 0, exceptionState);
+        Vector<v8::Local<v8::Value>> loggerArgs = toImplArguments<Vector<v8::Local<v8::Value>>>(info, 0, exceptionState);
         contextData->activityLogger()->logMethod("{{interface_name}}.{{method.name}}", info.Length(), loggerArgs.data());
     }
     {% endif %}