- Electron version: 1.2.8
- Operating system: Windows

Hi,

I've been trying to get a context menu containing some [predefined web contents roles](https://github.com/electron/electron/blob/master/lib/browser/api/menu-item-roles.js#L17) working for an application where we have multiple windows simultaneously. I've noticed that when a context menu is opened for a window that was created later than others, the role commands don't seem to execute when clicked. However, if don't use a role and instead define a click handler that calls the command on the web contents manually, it behaves normally.

I've been doing some digging and it seems that the reason is because, for a role, [`electron.webContents.getFocusedWebContents`](https://github.com/electron/electron/blob/master/lib/browser/api/web-contents.js#L257) is used to determine which web contents to call the command on (see [menu.js](https://github.com/electron/electron/blob/master/lib/browser/api/menu.js#L121)).

This function iterates through all existing web contents, then returns the first in the collection that is in a `webview`, otherwise the first that returns `true` from `contents.isFocused()`. However, it seems to be entirely possible that there are web contents other than the one that the context menu was raised for, who think they are focused (or perhaps are within a `webview`), and who were created earlier and therefore appear earlier in the collection.

This means there are situations when the 'wrong' web contents is returned from `getFocusedWebContents`, and therefore the role command is called on that 'wrong' web contents, which leads to the unexpected behaviour described above.

Is this a bug? And if so, is there a fix and/or workaround for this? I'm happy to contribute a PR if needed.

atom/browser/api/atom_api_web_contents.cc
content::WebContents* web_contents,
    const GURL& security_origin,
    content::MediaStreamType type) {
  return true;
}
void WebContents::RequestMediaAccessPermission(
    content::WebContents* web_contents,
    const content::MediaStreamRequest& request,
    const content::MediaResponseCallback& callback) {
  auto permission_helper =
      WebContentsPermissionHelper::FromWebContents(web_contents);
  permission_helper->RequestMediaAccessPermission(request, callback);
}
void WebContents::RequestToLockMouse(
    content::WebContents* web_contents,
    bool user_gesture,
    bool last_unlocked_by_target) {
  auto permission_helper =
      WebContentsPermissionHelper::FromWebContents(web_contents);
  permission_helper->RequestPointerLockPermission(user_gesture);
}
std::unique_ptr<content::BluetoothChooser> WebContents::RunBluetoothChooser(