* 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
content::WebContents* devtools) {
  if (!managed_devtools_web_contents_)
    external_devtools_web_contents_ = devtools;
}
void InspectableWebContentsImpl::ShowDevTools() {
  if (embedder_message_dispatcher_) {
    if (managed_devtools_web_contents_)
      view_->ShowDevTools();
    return;
  }
  
  
  embedder_message_dispatcher_.reset(
      DevToolsEmbedderMessageDispatcher::CreateForDevToolsFrontend(this));
  if (!external_devtools_web_contents_) {  
    managed_devtools_web_contents_.reset(
        content::WebContents::Create(content::WebContents::CreateParams(
            web_contents_->GetBrowserContext())));
    managed_devtools_web_contents_->SetDelegate(this);
  }
  Observe(GetDevToolsWebContents());
  AttachTo(content::DevToolsAgentHost::GetOrCreateFor(web_contents_.get()));
  GetDevToolsWebContents()->GetController().LoadURL(
      GetDevToolsURL(can_dock_), content::Referrer(),
      ui::PAGE_TRANSITION_AUTO_TOPLEVEL, std::string());
}
void InspectableWebContentsImpl::CloseDevTools() {