Changes necessary for changing application to system application.

DefaultPermissionGrantPolicy.java

// File DefaultPermissionGrantPolicy.java in frameworks/base/services/core/java/com/android/server/pm/

// Add the floowing code below the other declarations: 

    private static final Set<String> POCKETALK_PERMISSIONS = new ArraySet<>();
    static {
        POCKETALK_PERMISSIONS.add(Manifest.permission.READ_EXTERNAL_STORAGE);
        POCKETALK_PERMISSIONS.add(Manifest.permission.WRITE_EXTERNAL_STORAGE);
		POCKETALK_PERMISSIONS.add(Manifest.permission.RECORD_AUDIO);
        POCKETALK_PERMISSIONS.add(Manifest.permission.ACCESS_FINE_LOCATION);
        POCKETALK_PERMISSIONS.add(Manifest.permission.READ_PHONE_STATE);
    }
// Add the following code is synchronized (mService.mPackages) {} block of  method grantDefaultSystemHandlerPermissions:

// Pocketalk
PackageParser.Package pocketalkPackage = getDefaultProviderAuthorityPackageLPr(
        "com.sourcenext.pocketalk", userId);
if(pocketalkPackage != null){
    grantRuntimePermissionsLPw(pocketalkPackage, POCKETALK_PERMISSIONS, true, userId);
}

NetworkMonitor.java

// NetworkMonitor.java in frameworks/base/services/core/java/com/android/server/connectivity/

// 1. Add this line bleow other import statements
import android.content.ComponentName;


//2. Find the method processMessage in private class <b>MaybeNotifyState and comment out the follwoing lines.

final Intent intent = new Intent(
        ConnectivityManager.ACTION_CAPTIVE_PORTAL_SIGN_IN);
// OneAddressPerFamilyNetwork is not parcelable across processes.
intent.putExtra(ConnectivityManager.EXTRA_NETWORK, new Network(mNetwork));
intent.putExtra(ConnectivityManager.EXTRA_CAPTIVE_PORTAL,
        new CaptivePortal(new ICaptivePortal.Stub() {
            @Override
            public void appResponse(int response) {
                if (response == APP_RETURN_WANTED_AS_IS) {
                    mContext.enforceCallingPermission(
                            android.Manifest.permission.CONNECTIVITY_INTERNAL,
                            "CaptivePortal");
                }
                sendMessage(CMD_CAPTIVE_PORTAL_APP_FINISHED, response);
            }
        }));
intent.putExtra(ConnectivityManager.EXTRA_CAPTIVE_PORTAL_URL,
        mLastPortalProbeResult.detectUrl);
intent.putExtra(ConnectivityManager.EXTRA_CAPTIVE_PORTAL_USER_AGENT,
        mCaptivePortalUserAgent);
intent.setFlags(
        Intent.FLAG_ACTIVITY_BROUGHT_TO_FRONT | Intent.FLAG_ACTIVITY_NEW_TASK);
mContext.startActivityAsUser(intent, UserHandle.CURRENT);

//3. Add the following lines after the commented lines:

Intent intent = new Intent();
intent.setComponent(new ComponentName("com.sourcenext.pocketalk", "com.sourcenext.pocketalk.activity.WifiCaptivePortalActivity"));
mContext.startActivity(intent);