### Issue Details

* **Electron Version:**
  * 3.x, 4.x, 5.x, 6.x
* **Operating System:**
  * All
* **Last Known Working Electron version:**:
  * 2.x

### Expected Behavior
When navigations occur, a new process should be created for the navigation.

### Actual Behavior
When a navigation occurs _during_ a preloads scripts execution the same process is re-used as Chromium does not think the navigation has been committed yet.  This causes a memory leak and all native node modules to break.

### To Reproduce
Fiddle: https://gist.github.com/MarshallOfSound/c89aa0037c3da114d44aa3a2d1a0fc24

### Screenshots
![image](https://user-images.githubusercontent.com/6634592/55097842-eb45dd00-5079-11e9-99bf-d49c0d997bca.png)

As you can see here there are three navigation loads, the second and the third one actually have the same process ID (and are running in the same process)
shell/browser/atom_browser_client.cc
return MediaCaptureDevicesDispatcher::GetInstance();
}
content::DevToolsManagerDelegate*
AtomBrowserClient::GetDevToolsManagerDelegate() {
  return new DevToolsManagerDelegate;
}
NotificationPresenter* AtomBrowserClient::GetNotificationPresenter() {
  if (!notification_presenter_) {
    notification_presenter_.reset(NotificationPresenter::Create());
  }
  return notification_presenter_.get();
}
content::PlatformNotificationService*
AtomBrowserClient::GetPlatformNotificationService(
    content::BrowserContext* browser_context) {
  if (!notification_service_) {
    notification_service_.reset(new PlatformNotificationService(this));
  }
  return notification_service_.get();
}
base::FilePath AtomBrowserClient::GetDefaultDownloadDirectory() {
  
  base::FilePath path;
  if (base::PathService::Get(base::DIR_HOME, &path))
    path = path.Append(FILE_PATH_LITERAL("Downloads"));
  return path;
}
scoped_refptr<network::SharedURLLoaderFactory>