Allow apps to downgrade importance in createNotificationChannel

import android.annotation.IntDef;

import android.annotation.NonNull;

import android.annotation.Nullable;

import android.annotation.SdkConstant;

import android.annotation.SystemService;

import android.annotation.TestApi;

import android.app.Notification.Builder;

import android.content.ComponentName;

import android.content.Context;

import android.content.Intent;

import android.content.pm.ParceledListSlice;

import android.graphics.drawable.Icon;

import android.net.Uri;

import android.os.Bundle;

import android.os.Handler;

import android.os.IBinder;

import android.os.Looper;

import android.os.Parcel;

import android.os.Parcelable;

import android.os.RemoteException;

import android.os.StrictMode;

import android.os.UserHandle;

import android.provider.Settings.Global;

import android.service.notification.NotificationListenerService.Ranking;

import android.service.notification.StatusBarNotification;

import android.service.notification.ZenModeConfig;

import android.util.ArraySet;

     * Creates a notification channel that notifications can be posted to.

     *

     * This can also be used to restore a deleted channel and to update an existing channel's

     * name and description.

     * name, description, and/or importance.

     *

     * <p>The name and description should only be changed if the locale changes

     * or in response to the user renaming this channel. For example, if a user has a channel

     * named 'John Doe' that represents messages from a 'John Doe', and 'John Doe' changes his name

     * to 'John Smith,' the channel can be renamed to match.

     *

     * <p>The importance of an existing channel will only be changed if the new importance is lower

     * than the current value and the user has not altered any settings on this channel.

     *

     * All other fields are ignored for channels that already exist.

     *

     * @param channel  the channel to create.  Note that the created channel may differ from this

            existing.setDescription(channel.getDescription());

            existing.setBlockableSystem(channel.isBlockableSystem());

            // Apps are allowed to downgrade channel importance if the user has not changed any

            // fields on this channel yet.

            if (existing.getUserLockedFields() == 0 &&

                    channel.getImportance() < existing.getImportance()) {

                existing.setImportance(channel.getImportance());

            }

            updateConfig();

            return;

        }