* Electron Version: 3.0.0-beta.1
* Operating System (Platform and Version): macOS 10.13.5
* Last known working Electron version: 2.0.3

**Expected Behavior**
Dev tools extension tabs should appear after being added with the `BrowserWindow.addDevToolsExtension` API. I specifically tested the React and Redux extensions. I can tell the React extension is getting installed but not being shown because the usual
> Download the React DevTools for a better development experience

warning is absent.

**Actual behavior**
Dev tools extension tabs do not appear.

**To Reproduce**
Manually obtain the extension paths following the instructions here:
https://electronjs.org/docs/tutorial/devtools-extension
and supply them to `addDevToolsExtensions`.

Alternately, use [electron-devtools-installer](https://github.com/MarshallOfSound/electron-devtools-installer), which I have a repro case for using just Redux here:
https://github.com/ajmacd/electron-quick-start-typescript

Working with 2.0.3:
```sh
$ git clone https://github.com/ajmacd/electron-quick-start-typescript -b 2.0.3-devtools-working 
$ cd electron-quick-start-typescript
$ npm install
$ npm start
```

Not working with 3.0.0-beta.1:
```sh
$ git checkout 3.0.0-beta.1-devtools-not-working
$ npm install
$ npm start
```
brightray/browser/inspectable_web_contents_impl.cc
if (web_contents->GetNativeView()) {
        display = display::Screen::GetScreen()
                      ->GetDisplayNearestView(web_contents->GetNativeView())
                      .bounds();
      } else {
        display = display::Screen::GetScreen()->GetPrimaryDisplay().bounds();
      }
      devtools_bounds_.set_x(display.x() +
                             (display.width() - devtools_bounds_.width()) / 2);
      devtools_bounds_.set_y(
          display.y() + (display.height() - devtools_bounds_.height()) / 2);
    }
  }
  view_.reset(CreateInspectableContentsView(this));
}
InspectableWebContentsImpl::~InspectableWebContentsImpl() {
  
  if (GetDevToolsWebContents()) {
    if (managed_devtools_web_contents_)
      managed_devtools_web_contents_->SetDelegate(nullptr);
    
    
    WebContentsDestroyed();
  }
  
}
InspectableWebContentsView* InspectableWebContentsImpl::GetView() const {
  return view_.get();
}
content::WebContents* InspectableWebContentsImpl::GetWebContents() const {