bindings: Support "attribute FrozenArray<T>?"

Adds a quick hack to support a case of "attribute FrozenArray<T>?".

Bug: 1028047
Change-Id: Ib3cecc4beb6bcc0fb0dbc667aca595454cc90c86
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1933866
Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718676}
static void HTMLElementAttributeAttributeGetter(const v8::FunctionCallbackInfo<v8::Value>& info) {
  v8::Local<v8::Object> holder = info.Holder();

  TestObject* impl = V8TestObject::ToImpl(holder);

  V8SetReturnValueFast(info, WTF::GetPtr(impl->htmlElementAttribute()), impl);
}

static void HTMLElementAttributeAttributeGetter(const v8::FunctionCallbackInfo<v8::Value>& info) {
  v8::Local<v8::Object> holder = info.Holder();

  TestObject* impl = V8TestObject::ToImpl(holder);

  V8SetReturnValueFast(info, WTF::GetPtr(impl->htmlElementAttribute()), impl);
}
