### 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
std::vector<std::string>* additional_schemes) {
  additional_schemes->push_back(content::kChromeDevToolsScheme);
}
void AtomBrowserClient::SiteInstanceDeleting(
    content::SiteInstance* site_instance) {
  
  
  for (auto iter = site_per_affinities_.begin();
       iter != site_per_affinities_.end(); ++iter) {
    if (iter->second == site_instance) {
      site_per_affinities_.erase(iter);
      break;
    }
  }
}
std::unique_ptr<net::ClientCertStore> AtomBrowserClient::CreateClientCertStore(
    content::ResourceContext* resource_context) {
#if defined(USE_NSS_CERTS)
  return std::make_unique<net::ClientCertStoreNSS>(
      net::ClientCertStoreNSS::PasswordDelegateFactory());
#elif defined(OS_WIN)
  return std::make_unique<net::ClientCertStoreWin>();
#elif defined(OS_MACOSX)
  return std::make_unique<net::ClientCertStoreMac>();
#elif defined(USE_OPENSSL)
  return std::unique_ptr<net::ClientCertStore>();
#endif
}
std::unique_ptr<device::LocationProvider>