* Output of `node_modules/.bin/electron --version`: v3.0.0-beta.8
* Operating System (Platform and Version): Windows 10 10.0.16299 Build 16299
* Output of `node_modules/.bin/electron --version` on last known working Electron version (if applicable): v2.0.8

**Expected Behavior**
Webview DevTools should open in a window that is properly sized.

**Actual behavior**
Webview DevTools open in window with minimal size and are therefore not visible.

**To Reproduce**
**Edit** Works in BrowserWindow.webContents.openDevTools() Works **not** in webView.openDevTools()

**Screenshots**
![too_small_devtools_window](https://user-images.githubusercontent.com/6893212/44841398-850fed80-ac43-11e8-8bed-849d45473683.png)

**Additional Information**
Only reproducible on Windows 10 10.0.16299 Build 16299. Works correctly on MacOS High Sierra 10.13.4

brightray/browser/inspectable_web_contents_impl.cc
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 {
  return web_contents_.get();
}
content::WebContents* InspectableWebContentsImpl::GetDevToolsWebContents()
    const {
  if (external_devtools_web_contents_)
    return external_devtools_web_contents_;
  else
    return managed_devtools_web_contents_.get();
}
void InspectableWebContentsImpl::InspectElement(int x, int y) {