* Electron Version: v3.0.0-nightly.20180818
* Operating System (Platform and Version): Windows 10 1803
* Last known working Electron version: v3.0.0-beta.5

**Expected Behavior**
webview will not be freezed

**Actual behavior**
webview freezed occasionlly on navigation

**To Reproduce**
1. clone https://github.com/KochiyaOcean/electron-bugs

2. run `electron .` using electron v3.0.0-nightly.20180818

3. run scripts below in devtools
```javascript
require('electron').remote.webContents.getAllWebContents()
```
![image](https://user-images.githubusercontent.com/8194131/44320386-bf77ce80-a47c-11e8-9371-4e89cec444db.png)
there are 3 webcontents (BrowserWindow, WebView, DevTool)

4. run scripts below in devtools
```javascript
document.querySelector('webview').addEventListener('did-finish-load', () => document.querySelector('webview').loadURL('http://dmm.com'))
document.querySelector('webview').loadURL('http://dmm.com')
```

5. webview will freeze occasionally, and call any method of webview will throw an error
![image](https://user-images.githubusercontent.com/8194131/44320462-0b2a7800-a47d-11e8-9b21-3033df0372c4.png)

6. run `require('electron').remote.webContents.getAllWebContents()` again, and there are only 2 webcontents left (webcontents of webview is removed)
![image](https://user-images.githubusercontent.com/8194131/44320488-3c0aad00-a47d-11e8-99db-634428b1198c.png)

**Additional Information**
This bug occurs easier on complex websites, such as https://amazon.com , https://ebay.com , etc.
atom/browser/api/atom_api_web_contents.cc
} else {
    content::WebContents::CreateParams params(session->browser_context());
    web_contents = content::WebContents::Create(params);
  }
  InitWithSessionAndOptions(isolate, web_contents, session, options);
}
void WebContents::InitZoomController(content::WebContents* web_contents,
                                     const mate::Dictionary& options) {
  WebContentsZoomController::CreateForWebContents(web_contents);
  zoom_controller_ = WebContentsZoomController::FromWebContents(web_contents);
  double zoom_factor;
  if (options.Get(options::kZoomFactor, &zoom_factor))
    zoom_controller_->SetDefaultZoomFactor(zoom_factor);
}
void WebContents::InitWithSessionAndOptions(v8::Isolate* isolate,
                                            content::WebContents* web_contents,
                                            mate::Handle<api::Session> session,
                                            const mate::Dictionary& options) {
  Observe(web_contents);
  InitWithWebContents(web_contents, session->browser_context(), IsGuest());
  managed_web_contents()->GetView()->SetDelegate(this);
  auto* prefs = web_contents->GetMutableRendererPrefs();
  prefs->accept_languages = g_browser_process->GetApplicationLocale();
#if defined(OS_LINUX) || defined(OS_WIN)
  
  CR_DEFINE_STATIC_LOCAL(
      const gfx::FontRenderParams, params,
      (gfx::GetFontRenderParams(gfx::FontRenderParamsQuery(), nullptr)));
  prefs->should_antialias_text = params.antialiasing;
  prefs->use_subpixel_positioning = params.subpixel_positioning;