* 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,
                                        IPC::Message* message) {
  
  EmitWithSender(channel, frame_host, message, args);
}
void WebContents::OnRendererMessageTo(content::RenderFrameHost* frame_host,
                                      bool send_to_all,
                                      int32_t web_contents_id,
                                      const std::string& channel,
                                      const base::ListValue& args) {
  auto* web_contents = mate::TrackableObject<WebContents>::FromWeakMapID(
      isolate(), web_contents_id);
  if (web_contents) {
    web_contents->SendIPCMessageWithSender(send_to_all, channel, args, ID());
  }
}
mate::Handle<WebContents> WebContents::CreateFrom(
    v8::Isolate* isolate,
    content::WebContents* web_contents) {
  
  auto* existing = TrackableObject::FromWrappedClass(isolate, web_contents);
  if (existing)
    return mate::CreateHandle(isolate, static_cast<WebContents*>(existing));
  
  return mate::CreateHandle(isolate,
                            new WebContents(isolate, web_contents, REMOTE));
}
mate::Handle<WebContents> WebContents::CreateFrom(