### 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
AtomBrowserClient::OverrideSystemLocationProvider() {
#if BUILDFLAG(OVERRIDE_LOCATION_PROVIDER)
  return std::make_unique<FakeLocationProvider>();
#else
  return nullptr;
#endif
}
network::mojom::NetworkContextPtr AtomBrowserClient::CreateNetworkContext(
    content::BrowserContext* browser_context,
    bool ,
    const base::FilePath& ) {
  if (!browser_context)
    return nullptr;
  return NetworkContextServiceFactory::GetForContext(browser_context)
      ->CreateNetworkContext();
}
network::mojom::NetworkContext* AtomBrowserClient::GetSystemNetworkContext() {
  DCHECK_CURRENTLY_ON(BrowserThread::UI);
  DCHECK(g_browser_process->system_network_context_manager());
  return g_browser_process->system_network_context_manager()->GetContext();
}
base::Optional<service_manager::Manifest>
AtomBrowserClient::GetServiceManifestOverlay(base::StringPiece name) {
  if (name == content::mojom::kBrowserServiceName)
    return GetElectronContentBrowserOverlayManifest();
  return base::nullopt;
}
std::vector<service_manager::Manifest>