### 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::RenderProcessHost* host) {
  int process_id = host->GetID();
  pending_processes_.erase(process_id);
  renderer_is_subframe_.erase(process_id);
  RemoveProcessPreferences(process_id);
}
void AtomBrowserClient::RenderProcessReady(content::RenderProcessHost* host) {
  render_process_host_pids_[host->GetID()] =
      base::GetProcId(host->GetProcess().Handle());
  if (delegate_) {
    static_cast<api::App*>(delegate_)->RenderProcessReady(host);
  }
}
void AtomBrowserClient::RenderProcessExited(
    content::RenderProcessHost* host,
    const content::ChildProcessTerminationInfo& info) {
  auto host_pid = render_process_host_pids_.find(host->GetID());
  if (host_pid != render_process_host_pids_.end()) {
    if (delegate_) {
      static_cast<api::App*>(delegate_)->RenderProcessDisconnected(
          host_pid->second);
    }
    render_process_host_pids_.erase(host_pid);
  }
}
void OnOpenExternal(const GURL& escaped_url, bool allowed) {