### 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::SiteInstance* site_instance,
                   const GURL& dest_url) {
  return site_instance->IsSameSiteWithURL(dest_url) ||
         
         
         
         (content::SiteInstance::GetSiteForURL(browser_context, dest_url) ==
          site_instance->GetSiteURL());
}
AtomBrowserClient* g_browser_client = nullptr;
base::LazyInstance<std::string>::DestructorAtExit
    g_io_thread_application_locale = LAZY_INSTANCE_INITIALIZER;
base::NoDestructor<std::string> g_application_locale;
void SetApplicationLocaleOnIOThread(const std::string& locale) {