### 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
#include "components/net_log/chrome_net_log.h"
#include "content/public/browser/browser_ppapi_host.h"
#include "content/public/browser/browser_task_traits.h"
#include "content/public/browser/client_certificate_delegate.h"
#include "content/public/browser/render_frame_host.h"
#include "content/public/browser/render_process_host.h"
#include "content/public/browser/render_view_host.h"
#include "content/public/browser/site_instance.h"
#include "content/public/browser/web_contents.h"
#include "content/public/common/content_paths.h"
#include "content/public/common/content_switches.h"
#include "content/public/common/service_names.mojom.h"
#include "content/public/common/url_constants.h"
#include "content/public/common/web_preferences.h"
#include "electron/buildflags/buildflags.h"
#include "electron/grit/electron_resources.h"
#include "net/base/escape.h"
#include "net/ssl/ssl_cert_request_info.h"
#include "ppapi/host/ppapi_host.h"
#include "printing/buildflags/buildflags.h"
#include "services/device/public/cpp/geolocation/location_provider.h"
#include "services/network/public/cpp/features.h"
#include "services/network/public/cpp/resource_request_body.h"
#include "shell/app/manifests.h"
#include "shell/browser/api/atom_api_app.h"
#include "shell/browser/api/atom_api_protocol_ns.h"
#include "shell/browser/api/atom_api_web_contents.h"
#include "shell/browser/atom_browser_context.h"
#include "shell/browser/atom_browser_main_parts.h"
#include "shell/browser/atom_navigation_throttle.h"