### Preflight Checklist

* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### Issue Details

* **Electron Version:**
  * Tested on electron 5.0.0, through 5.0.6
* **Operating System:**
  * Windows 10 (Tested on both 1803 and 1809)

### Expected Behavior
`process.windowsStore` should return true if running inside of an appx package, as described in https://electronjs.org/docs/api/process#processwindowsstore

### Actual Behavior
`process.windowsStore` returns undefined, even when running in an appx package

### To Reproduce
I forked electron-quick-start to demonstrate the issue I found.
[https://github.com/dangeredwolf/electron-quick-start](https://github.com/dangeredwolf/electron-quick-start)

You can then use `npm run buildWindows` to create the appx.

If you're unfamiliar with appx deployment, appx files need to be signed to be installed, even in developer mode. [This is basically how to do that (from Microsoft's docs)](https://docs.microsoft.com/en-gb/windows/uwp/packaging/sign-app-package-using-signtool)

`process.windowsStore` is undefined in both the main and renderer processes when installed as an AppX

### Screenshots

I set it up to throw a dialog box of whatever process.windowsStore is

![image](https://user-images.githubusercontent.com/2636265/57185775-bb230280-6e9f-11e9-901b-0bb384de9fe8.png)

It's obvious from electron itself that it's running from C:\Program Files\WindowsApps

![image](https://user-images.githubusercontent.com/2636265/57185783-d726a400-6e9f-11e9-8d05-bfc38a959897.png)

### Additional Information

After further testing, I confirmed that this is an issue introduced in Electron 5.0.0. You can test this by cloning [the electron-quick-start fork with process.windowsStore checks](https://github.com/dangeredwolf/electron-quick-start) and changing `package.json`'s `"devDependencies"`>`"electron"` from `"^5.0.0"` to `"^4.2.0"`

![image](https://user-images.githubusercontent.com/2636265/57185900-e9561180-6ea2-11e9-84b7-75a4e3ef7a48.png)
shell/common/application_info_win.cc
#include "shell/common/application_info.h"
#include <windows.h>  
#include <VersionHelpers.h>
#include <appmodel.h>
#include <shlobj.h>
#include <memory>
#include "base/file_version_info.h"
#include "base/strings/string_util.h"
#include "base/strings/stringprintf.h"
#include "base/strings/utf_string_conversions.h"
#include "shell/browser/win/scoped_hstring.h"
namespace electron {
namespace {
base::string16 g_app_user_model_id;
}
const wchar_t kAppUserModelIDFormat[] = L"electron.app.$1";
std::string GetApplicationName() {
  auto* module = GetModuleHandle(nullptr);
  std::unique_ptr<FileVersionInfo> info(
      FileVersionInfo::CreateFileVersionInfoForModule(module));
  return base::UTF16ToUTF8(info->product_name());
}
std::string GetApplicationVersion() {