### 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
process_preferences_.erase(process_id);
}
bool AtomBrowserClient::IsProcessObserved(int process_id) const {
  return process_preferences_.find(process_id) != process_preferences_.end();
}
bool AtomBrowserClient::IsRendererSandboxed(int process_id) const {
  auto it = process_preferences_.find(process_id);
  return it != process_preferences_.end() && it->second.sandbox;
}
bool AtomBrowserClient::RendererUsesNativeWindowOpen(int process_id) const {
  auto it = process_preferences_.find(process_id);
  return it != process_preferences_.end() && it->second.native_window_open;
}
bool AtomBrowserClient::RendererDisablesPopups(int process_id) const {
  auto it = process_preferences_.find(process_id);
  return it != process_preferences_.end() && it->second.disable_popups;
}
std::string AtomBrowserClient::GetAffinityPreference(
    content::RenderFrameHost* rfh) const {
  auto* web_contents = content::WebContents::FromRenderFrameHost(rfh);
  auto* web_preferences = WebContentsPreferences::From(web_contents);
  std::string affinity;
  if (web_preferences &&
      web_preferences->GetPreference("affinity", &affinity) &&
      !affinity.empty()) {
    affinity = base::ToLowerASCII(affinity);
  }
  return affinity;
}
content::SiteInstance* AtomBrowserClient::GetSiteInstanceFromAffinity(