### 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 "shell/browser/atom_paths.h"
#include "shell/browser/atom_quota_permission_context.h"
#include "shell/browser/atom_speech_recognition_manager_delegate.h"
#include "shell/browser/child_web_contents_tracker.h"
#include "shell/browser/font_defaults.h"
#include "shell/browser/media/media_capture_devices_dispatcher.h"
#include "shell/browser/native_window.h"
#include "shell/browser/net/network_context_service.h"
#include "shell/browser/net/network_context_service_factory.h"
#include "shell/browser/net/proxying_url_loader_factory.h"
#include "shell/browser/net/system_network_context_manager.h"
#include "shell/browser/notifications/notification_presenter.h"
#include "shell/browser/notifications/platform_notification_service.h"
#include "shell/browser/session_preferences.h"
#include "shell/browser/ui/devtools_manager_delegate.h"
#include "shell/browser/web_contents_permission_helper.h"
#include "shell/browser/web_contents_preferences.h"
#include "shell/browser/window_list.h"
#include "shell/common/application_info.h"
#include "shell/common/options_switches.h"
#include "shell/common/platform_util.h"
#include "ui/base/l10n/l10n_util.h"
#include "ui/base/resource/resource_bundle.h"
#include "ui/native_theme/native_theme.h"
#include "v8/include/v8.h"
#if defined(OS_WIN)
#include "sandbox/win/src/sandbox_policy.h"
#endif
#if defined(USE_NSS_CERTS)
#include "net/ssl/client_cert_store_nss.h"