### Preflight Checklist
* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### Issue Details

* **Electron Version:**
  * 10.1.1
* **Operating System:**
  * macOS 10.15.4

We recently started launching as hidden on macOS (that is, `show: false` or `browserWindow.hide()` while loading the page, followed by `browserWindow.show()` when the dock icon is clicked). This results in some busted focus behavior on the first activation of the window. The second activation restores it.

### Expected Behavior
The guest page receives a `focus` event on the first activation of the app, when created with `show: false`.

### Actual Behavior
The guest page doesn't receive the first `focus` event. Subsequent activations do trigger a `focus` event.

### To Reproduce
[Electron Fiddle](https://gist.github.com/CharlieHess/c507468cd40630d04f58c6514100b997)

shell/browser/api/electron_api_web_contents.cc
v8::Local<v8::Value> message_value,
                              base::Optional<v8::Local<v8::Value>> transfer) {
  v8::Isolate* isolate = JavascriptEnvironment::GetIsolate();
  blink::TransferableMessage transferable_message;
  if (!electron::SerializeV8Value(isolate, message_value,
                                  &transferable_message)) {
     SerializeV8Value sets an exception.
    return;
  }
  std::vector<gin::Handle<MessagePort>> wrapped_ports;
  if (transfer) {
    if (!gin::ConvertFromV8(isolate, *transfer, &wrapped_ports)) {
      isolate->ThrowException(v8::Exception::Error(
          gin::StringToV8(isolate, "Invalid value for transfer")));
      return;
    }
  }
  bool threw_exception = false;
  transferable_message.ports =
      MessagePort::DisentanglePorts(isolate, wrapped_ports, &threw_exception);
  if (threw_exception)
    return;
  content::RenderFrameHost* frame_host = ontents()->GetMainFrame();
  mojo::AssociatedRemote<mojom::ElectronRenderer> electron_renderer;
  frame_host->GetRemoteAssociatedInterfaces()->GetInterface(&electron_renderer);
  electron_renderer->ReceivePostMessage(channel,
                                        std::move(transferable_message));
}
void WebContents::MessageSync(bool internal,