### 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
content::BrowserContext* browser_context,
    content::SiteInstance* current_instance,
    content::SiteInstance* speculative_instance,
    const GURL& dest_url,
    bool has_response_started) const {
  bool navigation_was_redirected = false;
  if (has_response_started) {
    navigation_was_redirected =
        !IsSameWebSite(browser_context, current_instance, dest_url);
  } else {
    navigation_was_redirected =
        speculative_instance &&
        !IsSameWebSite(browser_context, speculative_instance, dest_url);
  }
  return navigation_was_redirected;
}
void AtomBrowserClient::AddProcessPreferences(
    int process_id,
    AtomBrowserClient::ProcessPreferences prefs) {
  process_preferences_[process_id] = prefs;
}
void AtomBrowserClient::RemoveProcessPreferences(int process_id) {