### 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
.SetMethod("detachFromOuterFrame", &Ws::DetachFromOuterFrame)
      .SetMethod("isOffscreen", &Ws::IsOffScreen)
#if BUILDFLAG(ENABLE_OSR)
      .SetMethod("startPainting", &Ws::StartPainting)
      .SetMethod("stopPainting", &Ws::StopPainting)
      .SetMethod("isPainting", &Ws::IsPainting)
      .SetMethod("_setFrameRate", &Ws::SetFrameRate)
      .SetMethod("_getFrameRate", &Ws::GetFrameRate)
      .SetProperty("frameRate", &Ws::GetFrameRate,
                   &Ws::SetFrameRate)
#endif
      .SetMethod("invalidate", &Ws::Invalidate)
      .SetMethod("_setZoomLevel", &Ws::SetZoomLevel)
      .SetMethod("_getZoomLevel", &Ws::GetZoomLevel)
      .SetProperty("zoomLevel", &Ws::GetZoomLevel,
                   &Ws::SetZoomLevel)
      .SetMethod("_setZoomFactor", &Ws::SetZoomFactor)
      .SetMethod("_getZoomFactor", &Ws::GetZoomFactor)
      .SetProperty("zoomFactor", &Ws::GetZoomFactor,
                   &Ws::SetZoomFactor)
      .SetMethod("getType", &Ws::GetType)
      .SetMethod("_getPreloadPaths", &Ws::GetPreloadPaths)
      .SetMethod("getWebPreferences", &Ws::GetWebPreferences)
      .SetMethod("getLastWebPreferences", &Ws::GetLastWebPreferences)
      .SetMethod("getOwnerBrowserWindow", &Ws::GetOwnerBrowserWindow)
      .SetMethod("inspectServiceWorker", &Ws::InspectServiceWorker)
      .SetMethod("inspectSharedWorker", &Ws::InspectSharedWorker)
      .SetMethod("inspectSharedWorkerById",
                 &Ws::InspectSharedWorkerById)
      .SetMethod("getAllSharedWorkers", &Ws::GetAllSharedWorkers)