### 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:**
10.0.0-nightly.20200220
* **Operating System:**
macOS 10.15.1
* **Last Known Working Electron version:**
I don't know (judging by implementation it never worked)

### Expected Behavior:
Call to BrowserWindow.webContents.focus focuses proper window

### Actual Behavior:
Call  to BrowserWindow.webContents.focus does nothing

### To Reproduce:

Run following simple app:
```
const { app, BrowserWindow } = require('electron')

function createWindow () {
  let win1 = new BrowserWindow({ x:100, y: 300, width: 300, height: 200 })
  win1.on('closed', () => {
    win1 = null
  })
  win1.loadURL('https://github.com')

  let win2 = new BrowserWindow({ x:300, y: 300, width: 300, height: 200 })
  win2.on('closed', () => {
    win1 = null
  })
  win2.loadURL('http://www.example.com')

  setTimeout(() => {
    win1.webContents.focus();
  }, 3000);
}

app.on('ready', createWindow)
```

It works as expected on Windows: it creates two windows and after three seconds it focuses the first one. On mac it doesn't work and call to `webContents.focus` doesn't change the focus (it stays on the second window).
shell/browser/api/electron_api_web_contents.cc
base::Value tab_id(ID());
  managed_ontents()->CallClientFunction("DevToolsAPI.setInspectedTabId",
                                             &tab_id, nullptr, nullptr);
  // Inherit owner window in devtools when it doesn't have one.
  auto* devtools = managed_ontents()->GetDevToolsWs();
  bool has_window = devtools->GetUserData(NativeWindowRelay::UserDataKey());
  if (owner_window() && !has_window)
    handle->SetOwnerWindow(devtools, owner_window());
  Emit("devtools-opened");
}
void Ws::DevToolsClosed() {
  v8::Locker locker(isolate());
  v8::HandleScope handle_scope(isolate());
  devtools_ontents_.Reset();
  Emit("devtools-closed");
}
bool Ws::OnMessageReceived(const IPC::Message& message) {
  bool handled = true;
  IPC_BEGIN_MESSAGE_MAP(Ws, message)
    IPC_MESSAGE_HANDLER_CODE(WidgetHostMsg_SetCursor, OnCursorChange,
                             handled = false)
    IPC_MESSAGE_UNHANDLED(handled = false)
  IPC_END_MESSAGE_MAP()
  return handled;
}
// There are three ways of destroying a ws:
// 1. call ws.destroy();
// 2. garbage collection;
// 3. user closes the window of ws;
// 4. the embedder detaches the frame.