* 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
GURL("chrome-guest://fake-host"));
    content::WebContents::CreateParams params(session->browser_context(),
                                              site_instance);
    guest_delegate_.reset(
        new WebViewGuestDelegate(embedder_->web_contents(), this));
    params.guest_delegate = guest_delegate_.get();
#if defined(ENABLE_OSR)
    if (embedder_ && embedder_->IsOffScreen()) {
      auto* view = new OffScreenWebContentsView(
          false, base::Bind(&WebContents::OnPaint, base::Unretained(this)));
      params.view = view;
      params.delegate_view = view;
      web_contents = content::WebContents::Create(params);
      view->SetWebContents(web_contents);
    } else {
#endif
      web_contents = content::WebContents::Create(params);
#if defined(ENABLE_OSR)
    }
  } else if (IsOffScreen()) {
    bool transparent = false;
    options.Get("transparent", &transparent);
    content::WebContents::CreateParams params(session->browser_context());
    auto* view = new OffScreenWebContentsView(
        transparent, base::Bind(&WebContents::OnPaint, base::Unretained(this)));
    params.view = view;
    params.delegate_view = view;
    web_contents = content::WebContents::Create(params);
    view->SetWebContents(web_contents);
#endif