[Android O] Only delete legacy notification channels on upgrade

chrome/android/java/src/org/chromium/chrome/browser/notifications/ChannelDefinitions.java

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chrome.browser.notifications;
 
 import android.annotation.TargetApi;
 import android.app.NotificationManager;
 import android.os.Build;
 import android.support.annotation.StringDef;
@@ skipping 15 matching lines @@
  */
 public class ChannelDefinitions {
     public static final String CHANNEL_ID_BROWSER = "browser";
     public static final String CHANNEL_ID_DOWNLOADS = "downloads";
     public static final String CHANNEL_ID_INCOGNITO = "incognito";
     public static final String CHANNEL_ID_MEDIA = "media";
     public static final String CHANNEL_ID_SITES = "sites";
     static final String CHANNEL_GROUP_ID_GENERAL = "general";
     /**
      * Version number identifying the current set of channels. This must be incremented whenever
-     * any channels are added or removed from the set of channels created in
-     * {@link ChannelsInitializer#initializeStartupChannels()}.
+     * the set of channels returned by {@link #getStartupChannelIds()} or
+     * {@link #getLegacyChannelIds()} changes.
      */
     static final int CHANNELS_VERSION = 0;
 
-    // To define a new channel, add the channel ID to this StringDef and add a new entry to
-    // PredefinedChannels.MAP below with the appropriate channel parameters.
+    /**
+     * To define a new channel, add the channel ID to this StringDef and add a new entry to
+     * PredefinedChannels.MAP below with the appropriate channel parameters.
+     * To remove an existing channel, remove the ID from this StringDef, remove its entry from
+     * Predefined Channels.MAP, and add the ID to the LEGACY_CHANNELS_ID array below.
+     */
     @StringDef({CHANNEL_ID_BROWSER, CHANNEL_ID_DOWNLOADS, CHANNEL_ID_INCOGNITO, CHANNEL_ID_MEDIA,
             CHANNEL_ID_SITES})
     @Retention(RetentionPolicy.SOURCE)
     public @interface ChannelId {}
 
     @StringDef({CHANNEL_GROUP_ID_GENERAL})
     @Retention(RetentionPolicy.SOURCE)
     @interface ChannelGroupId {}
 
     // Map defined in static inner class so it's only initialized lazily.
     @TargetApi(Build.VERSION_CODES.N) // for NotificationManager.IMPORTANCE_* constants
     private static class PredefinedChannels {
         /**
          * The set of predefined channels to be initialized on startup. CHANNELS_VERSION must be
          * incremented every time an entry is modified, removed or added to this map.
+         * If an entry is removed from here then it must be added to the LEGACY_CHANNEL_IDs array.
          */
         static final Map<String, Channel> MAP;
         static {
             Map<String, Channel> map = new HashMap<>();
             map.put(CHANNEL_ID_BROWSER,
                     new Channel(CHANNEL_ID_BROWSER,
                             org.chromium.chrome.R.string.notification_category_browser,
                             NotificationManager.IMPORTANCE_LOW, CHANNEL_GROUP_ID_GENERAL));
             map.put(CHANNEL_ID_DOWNLOADS,
                     new Channel(CHANNEL_ID_DOWNLOADS,
                             org.chromium.chrome.R.string.notification_category_downloads,
                             NotificationManager.IMPORTANCE_LOW, CHANNEL_GROUP_ID_GENERAL));
             map.put(CHANNEL_ID_INCOGNITO,
                     new Channel(CHANNEL_ID_INCOGNITO,
                             org.chromium.chrome.R.string.notification_category_incognito,
                             NotificationManager.IMPORTANCE_LOW, CHANNEL_GROUP_ID_GENERAL));
             map.put(CHANNEL_ID_MEDIA,
                     new Channel(CHANNEL_ID_MEDIA,
                             org.chromium.chrome.R.string.notification_category_media,
                             NotificationManager.IMPORTANCE_LOW, CHANNEL_GROUP_ID_GENERAL));
             map.put(CHANNEL_ID_SITES,
                     new Channel(CHANNEL_ID_SITES,
                             org.chromium.chrome.R.string.notification_category_sites,
                             NotificationManager.IMPORTANCE_DEFAULT, CHANNEL_GROUP_ID_GENERAL));
             MAP = Collections.unmodifiableMap(map);
         }
     }
 
+    /**
+     * When channels become deprecated they should be removed from PredefinedChannels and their ids
+     * added to this array so they can be deleted on upgrade.
+     * We also want to keep track of old channel ids so they aren't accidentally reused.
+     */
+    private static final String[] LEGACY_CHANNEL_IDS = {};
+
     // Map defined in static inner class so it's only initialized lazily.
     private static class PredefinedChannelGroups {
         static final Map<String, ChannelGroup> MAP;
         static {
             Map<String, ChannelGroup> map = new HashMap<>();
             map.put(CHANNEL_GROUP_ID_GENERAL,
                     new ChannelGroup(CHANNEL_GROUP_ID_GENERAL,
                             org.chromium.chrome.R.string.notification_category_group_general));
             MAP = Collections.unmodifiableMap(map);
         }
     }
 
+    /**
+     * @return A set of channel ids of channels that should be initialized on startup.
+     */
     Set<String> getStartupChannelIds() {
         // CHANNELS_VERSION must be incremented if the set of channels returned here changes.
         return PredefinedChannels.MAP.keySet();
     }
 
+    /**
+     * @return An array of old ChannelIds that may have been returned by
+     * {@link #getStartupChannelIds} in the past, but are no longer in use.
+     */
+    public String[] getLegacyChannelIds() {
+        return LEGACY_CHANNEL_IDS;
+    }
+
     ChannelGroup getChannelGroupFromId(Channel channel) {
         return PredefinedChannelGroups.MAP.get(channel.mGroupId);
     }
 
     Channel getChannelFromId(@ChannelId String channelId) {
         return PredefinedChannels.MAP.get(channelId);
     }
 
     /**
      * Helper class containing notification channel properties.
@@ skipping 22 matching lines @@
         @ChannelGroupId
         final String mId;
         final int mNameResId;
 
         ChannelGroup(@ChannelGroupId String id, int nameResId) {
             this.mId = id;
             this.mNameResId = nameResId;
         }
     }
 }