* 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
web_contents()->SetAudioMuted(muted);
}
bool WebContents::IsAudioMuted() {
  return web_contents()->IsAudioMuted();
}
bool WebContents::IsCurrentlyAudible() {
  return web_contents()->IsCurrentlyAudible();
}
void WebContents::Print(mate::Arguments* args) {
  PrintSettings settings = {false, false, base::string16()};
  if (args->Length() >= 1 && !args->GetNext(&settings)) {
    args->ThrowError();
    return;
  }
  auto* print_view_manager_basic_ptr =
      printing::PrintViewManagerBasic::FromWebContents(web_contents());
  if (args->Length() == 2) {
    base::Callback<void(bool)> callback;
    if (!args->GetNext(&callback)) {
      args->ThrowError();
      return;
    }
    print_view_manager_basic_ptr->SetCallback(callback);
  }
  print_view_manager_basic_ptr->PrintNow(
      web_contents()->GetMainFrame(), settings.silent,
      settings.print_background, settings.device_name);
}
std::vector<printing::PrinterBasicInfo> WebContents::GetPrinterList() {