* 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
content::RenderFrameHost* frame_host) {
  bool handled = true;
  FrameDispatchHelper helper = {this, frame_host};
  IPC_BEGIN_MESSAGE_MAP_WITH_PARAM(WebContents, message, frame_host)
    IPC_MESSAGE_HANDLER(AtomFrameHostMsg_Message, OnRendererMessage)
    IPC_MESSAGE_FORWARD_DELAY_REPLY(AtomFrameHostMsg_Message_Sync, &helper,
                                    FrameDispatchHelper::OnRendererMessageSync)
    IPC_MESSAGE_HANDLER(AtomFrameHostMsg_Message_To, OnRendererMessageTo)
    IPC_MESSAGE_FORWARD_DELAY_REPLY(
        AtomFrameHostMsg_SetTemporaryZoomLevel, &helper,
        FrameDispatchHelper::OnSetTemporaryZoomLevel)
    IPC_MESSAGE_FORWARD_DELAY_REPLY(AtomFrameHostMsg_GetZoomLevel, &helper,
                                    FrameDispatchHelper::OnGetZoomLevel)
#if defined(TOOLKIT_VIEWS) && !defined(OS_MACOSX)
    IPC_MESSAGE_HANDLER(AtomAutofillFrameHostMsg_ShowPopup, ShowAutofillPopup)
    IPC_MESSAGE_HANDLER(AtomAutofillFrameHostMsg_HidePopup, HideAutofillPopup)
#endif
    IPC_MESSAGE_UNHANDLED(handled = false)
  IPC_END_MESSAGE_MAP()
  return handled;
}
void WebContents::WebContentsDestroyed() {