### 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("inspectElement", &Ws::InspectElement)
      .SetMethod("setIgnoreMenuShortcuts", &Ws::SetIgnoreMenuShortcuts)
      .SetMethod("_setAudioMuted", &Ws::SetAudioMuted)
      .SetMethod("_isAudioMuted", &Ws::IsAudioMuted)
      .SetProperty("audioMuted", &Ws::IsAudioMuted,
                   &Ws::SetAudioMuted)
      .SetMethod("isCurrentlyAudible", &Ws::IsCurrentlyAudible)
      .SetMethod("undo", &Ws::Undo)
      .SetMethod("redo", &Ws::Redo)
      .SetMethod("cut", &Ws::Cut)
      .SetMethod("copy", &Ws::Copy)
      .SetMethod("paste", &Ws::Paste)
      .SetMethod("pasteAndMatchStyle", &Ws::PasteAndMatchStyle)
      .SetMethod("delete", &Ws::Delete)
      .SetMethod("selectAll", &Ws::SelectAll)
      .SetMethod("unselect", &Ws::Unselect)
      .SetMethod("replace", &Ws::Replace)
      .SetMethod("replaceMisspelling", &Ws::ReplaceMisspelling)
      .SetMethod("findInPage", &Ws::FindInPage)
      .SetMethod("stopFindInPage", &Ws::StopFindInPage)
      .SetMethod("focus", &Ws::Focus)
      .SetMethod("isFocused", &Ws::IsFocused)
      .SetMethod("tabTraverse", &Ws::TabTraverse)
      .SetMethod("_send", &Ws::SendIPCMessage)
      .SetMethod("_sendToFrame", &Ws::SendIPCMessageToFrame)
      .SetMethod("sendInputEvent", &Ws::SendInputEvent)
      .SetMethod("beginFrameSubscription", &Ws::BeginFrameSubscription)
      .SetMethod("endFrameSubscription", &Ws::EndFrameSubscription)
      .SetMethod("startDrag", &Ws::StartDrag)
      .SetMethod("attachToIframe", &Ws::AttachToIframe)