* 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 std::string& origin,
    const std::string& script) {
  extensions_api_[origin + "/"] = script;
}
void InspectableWebContentsImpl::HandleMessageFromDevToolsFrontend(
    const std::string& message) {
  
  if (!embedder_message_dispatcher_) {
    return;
  }
  std::string method;
  base::ListValue empty_params;
  base::ListValue* params = &empty_params;
  base::DictionaryValue* dict = nullptr;
  std::unique_ptr<base::Value> parsed_message(base::JSONReader::Read(message));
  if (!parsed_message || !parsed_message->GetAsDictionary(&dict) ||
      !dict->GetString(kFrontendHostMethod, &method) ||
      (dict->HasKey(kFrontendHostParams) &&
       !dict->GetList(kFrontendHostParams, &params))) {
    LOG(ERROR) << "Invalid message was sent to embedder: " << message;
    return;
  }
  int id = 0;
  dict->GetInteger(kFrontendHostId, &id);
  embedder_message_dispatcher_->Dispatch(
      base::Bind(&InspectableWebContentsImpl::SendMessageAck,
                 weak_factory_.GetWeakPtr(), id),
      method, params);
}
void InspectableWebContentsImpl::DispatchProtocolMessage(