refactor: declare gin::Wrapper subclasses as final (#43527)

As per the gin docs: "Wrappable<T> explicitly does not support further
subclassing of T. Subclasses of Wrappable<T> should be declared final."

shell/browser/api/electron_api_web_contents.cc

@@ -1902,7 +1902,7 @@ namespace {
 // This object wraps the InvokeCallback so that if it gets GC'd by V8, we can
 // still call the callback and send an error. Not doing so causes a Mojo DCHECK,
 // since Mojo requires callbacks to be called before they are destroyed.
-class ReplyChannel : public gin::Wrappable<ReplyChannel> {
+class ReplyChannel final : public gin::Wrappable<ReplyChannel> {
  public:
   using InvokeCallback = electron::mojom::ElectronApiIPC::InvokeCallback;
   static gin::Handle<ReplyChannel> Create(v8::Isolate* isolate,