toImplArguments should return HeapVector for Union types.

Source/bindings/templates/methods.cpp

 {% from 'conversions.cpp' import declare_enum_validation_variable, v8_value_to_local_cpp_value %}
 
 
 {##############################################################################}
 {% macro generate_method(method, world_suffix) %}
 {% filter conditional(method.conditional_string) %}
 {% if method.returns_promise and method.has_exception_state %}
 static void {{method.name}}{{method.overload_index}}Method{{world_suffix}}Promise(const v8::FunctionCallbackInfo<v8::Value>& info, ExceptionState& exceptionState)
 {% else %}
 static void {{method.name}}{{method.overload_index}}Method{{world_suffix}}(const v8::FunctionCallbackInfo<v8::Value>& info)
@@ skipping 448 matching lines @@
     {% endif %}{# not method.overloads #}
     {% if world_suffix in method.activity_logging_world_list %}
     ScriptState* scriptState = ScriptState::from(info.GetIsolate()->GetCurrentContext());
     V8PerContextData* contextData = scriptState->perContextData();
     {% if method.activity_logging_world_check %}
     if (scriptState->world().isIsolatedWorld() && contextData && contextData->activityLogger())
     {% else %}
     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 %}
     {% if method.is_custom %}
     {{v8_class}}::{{method.name}}MethodCustom(info);
     {% elif method.is_post_message %}
     postMessageMethodCommon("{{interface_name}}", {{v8_class}}::toImpl(info.Holder()), info);
     {% else %}
     {{cpp_class_or_partial}}V8Internal::{{method.name}}Method{{world_suffix}}(info);
     {% endif %}
@@ skipping 182 matching lines @@
                           if method.overloads else
                           method.runtime_enabled_function) %}
 v8::Local<v8::FunctionTemplate> functionTemplate = v8::FunctionTemplate::New(isolate, {{cpp_class_or_partial}}V8Internal::{{method.name}}MethodCallback, v8Undefined(), defaultSignature, {{method.number_of_required_arguments}});
 v8::Local<v8::Function> function = ->GetFunction(isolate->GetCurrentContext())).ToLocalChecked();
 v8CallOrCrash(prototypeObject->Set(isolate->GetCurrentContext(), v8AtomicString(isolate, "{{method.name}}"), function));
 {% endfilter %}{# runtime_enabled() #}
 {% endfilter %}{# exposed() #}
 {% endfor %}
 {% endif %}
 {%- endmacro %}