### 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 custom_margins(base::Value::Type::DICTIONARY);
      int top = 0;
      margins.Get("top", &top);
      custom_margins.SetIntKey(printing::kSettingMarginTop, top);
      int bottom = 0;
      margins.Get("bottom", &bottom);
      custom_margins.SetIntKey(printing::kSettingMarginBottom, bottom);
      int left = 0;
      margins.Get("left", &left);
      custom_margins.SetIntKey(printing::kSettingMarginLeft, left);
      int right = 0;
      margins.Get("right", &right);
      custom_margins.SetIntKey(printing::kSettingMarginRight, right);
      settings.SetPath(printing::kSettingMarginsCustom,
                       std::move(custom_margins));
    }
  } else {
    settings.SetIntKey(printing::kSettingMarginsType,
                       printing::DEFAULT_MARGINS);
  }
  // Set whether to print color or greyscale
  bool print_color = true;
  options.Get("color", &print_color);
  int color_setting = print_color ? printing::COLOR : printing::GRAY;
  settings.SetIntKey(printing::kSettingColor, color_setting);
  // Is the orientation landscape or portrait.
  bool landscape = false;
  options.Get("landscape", &landscape);
  settings.SetBoolKey(printing::kSettingLandscape, landscape);
  // We set the default to the system's default printer and only update