* 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
.SetMethod("_send", &WebContents::SendIPCMessage)
      .SetMethod("sendInputEvent", &WebContents::SendInputEvent)
      .SetMethod("beginFrameSubscription", &WebContents::BeginFrameSubscription)
      .SetMethod("endFrameSubscription", &WebContents::EndFrameSubscription)
      .SetMethod("startDrag", &WebContents::StartDrag)
      .SetMethod("isGuest", &WebContents::IsGuest)
      .SetMethod("attachToIframe", &WebContents::AttachToIframe)
      .SetMethod("isOffscreen", &WebContents::IsOffScreen)
      .SetMethod("startPainting", &WebContents::StartPainting)
      .SetMethod("stopPainting", &WebContents::StopPainting)
      .SetMethod("isPainting", &WebContents::IsPainting)
      .SetMethod("setFrameRate", &WebContents::SetFrameRate)
      .SetMethod("getFrameRate", &WebContents::GetFrameRate)
      .SetMethod("invalidate", &WebContents::Invalidate)
      .SetMethod("setZoomLevel", &WebContents::SetZoomLevel)
      .SetMethod("_getZoomLevel", &WebContents::GetZoomLevel)
      .SetMethod("setZoomFactor", &WebContents::SetZoomFactor)
      .SetMethod("_getZoomFactor", &WebContents::GetZoomFactor)
      .SetMethod("getType", &WebContents::GetType)
      .SetMethod("_getPreloadPath", &WebContents::GetPreloadPath)
      .SetMethod("getWebPreferences", &WebContents::GetWebPreferences)
      .SetMethod("getLastWebPreferences", &WebContents::GetLastWebPreferences)
      .SetMethod("getOwnerBrowserWindow", &WebContents::GetOwnerBrowserWindow)
      .SetMethod("hasServiceWorker", &WebContents::HasServiceWorker)
      .SetMethod("unregisterServiceWorker",
                 &WebContents::UnregisterServiceWorker)
      .SetMethod("inspectServiceWorker", &WebContents::InspectServiceWorker)
      .SetMethod("print", &WebContents::Print)
      .SetMethod("getPrinters", &WebContents::GetPrinterList)
      .SetMethod("_printToPDF", &WebContents::PrintToPDF)