* 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
const std::string& channel,
                                           const base::ListValue& args,
                                           int32_t sender_id) {
  auto* frame_host = web_contents()->GetMainFrame();
  if (frame_host) {
    return frame_host->Send(new AtomFrameMsg_Message(
        frame_host->GetRoutingID(), all_frames, channel, args, sender_id));
  }
  return false;
}
void WebContents::SendInputEvent(v8::Isolate* isolate,
                                 v8::Local<v8::Value> input_event) {
  content::RenderWidgetHostView* view =
      web_contents()->GetRenderWidgetHostView();
  if (!view)
    return;
  content::RenderWidgetHost* rwh = view->GetRenderWidgetHost();
  blink::WebInputEvent::Type type =
      mate::GetWebInputEventType(isolate, input_event);
  if (blink::WebInputEvent::IsMouseEventType(type)) {
    blink::WebMouseEvent mouse_event;
    if (mate::ConvertFromV8(isolate, input_event, &mouse_event)) {
      if (IsOffScreen()) {
#if defined(ENABLE_OSR)
        GetOffScreenRenderWidgetHostView()->SendMouseEvent(mouse_event);
#endif
      } else {