* 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 gfx::RectF& bounds,
                                    const std::vector<base::string16>& values,
                                    const std::vector<base::string16>& labels) {
  bool offscreen = IsOffScreen() || (embedder_ && embedder_->IsOffScreen());
  gfx::RectF popup_bounds(bounds);
  content::RenderFrameHost* embedder_frame_host = nullptr;
  if (embedder_) {
    auto* embedder_view = embedder_->web_contents()->GetMainFrame()->GetView();
    auto* view = web_contents()->GetMainFrame()->GetView();
    auto offset = view->GetViewBounds().origin() -
                  embedder_view->GetViewBounds().origin();
    popup_bounds.Offset(offset.x(), offset.y());
    embedder_frame_host = embedder_->web_contents()->GetMainFrame();
  }
  CommonWebContentsDelegate::ShowAutofillPopup(
      frame_host, embedder_frame_host, offscreen, popup_bounds, values, labels);
}
#endif
bool WebContents::OnMessageReceived(const IPC::Message& message) {
  bool handled = true;
  IPC_BEGIN_MESSAGE_MAP(WebContents, message)
    IPC_MESSAGE_HANDLER_CODE(ViewHostMsg_SetCursor, OnCursorChange,
                             handled = false)
    IPC_MESSAGE_UNHANDLED(handled = false)
  IPC_END_MESSAGE_MAP()
  return handled;
}
bool WebContents::OnMessageReceived(const IPC::Message& message,