* 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
const DispatchCallback& callback,
    const std::string& browser_id,
    const std::string& url) {
  callback.Run(nullptr);
}
void InspectableWebContentsImpl::GetPreferences(
    const DispatchCallback& callback) {
  const base::DictionaryValue* prefs =
      pref_service_->GetDictionary(kDevToolsPreferences);
  callback.Run(prefs);
}
void InspectableWebContentsImpl::SetPreference(const std::string& name,
                                               const std::string& value) {
  DictionaryPrefUpdate update(pref_service_, kDevToolsPreferences);
  update.Get()->SetKey(name, base::Value(value));
}
void InspectableWebContentsImpl::RemovePreference(const std::string& name) {
  DictionaryPrefUpdate update(pref_service_, kDevToolsPreferences);
  update.Get()->RemoveWithoutPathExpansion(name, nullptr);
}
void InspectableWebContentsImpl::ClearPreferences() {
  DictionaryPrefUpdate update(pref_service_, kDevToolsPreferences);
  update.Get()->Clear();
}
void InspectableWebContentsImpl::ConnectionReady() {}
void InspectableWebContentsImpl::RegisterExtensionsAPI(