WebLayer: add MediaSession notification channel matching Chrome's.

Bug: 1066263
Change-Id: I4548f13ad9e34b0b64c8d09e006c2cfa0dca365e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2260877
Commit-Queue: Evan Stade <estade@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781945}

chrome/browser/ui/android/strings/android_chrome_strings.grd

@@ -251,9 +251,6 @@ CHAR-LIMIT guidelines:
       <message name="IDS_NOTIFICATION_CATEGORY_ANNOUNCEMENT" desc="Label for announcements notifications, within a list of notification categories. [CHAR-LIMIT=32]">
         Announcements
       </message>
-      <message name="IDS_NOTIFICATION_CATEGORY_MEDIA_PLAYBACK" desc="Label for media playback notifications, within a list of notification categories. [CHAR-LIMIT=32]">
-        Playing media
-      </message>
 
       <message name="IDS_NOTIFICATION_CATEGORY_PERMISSION_REQUESTS" desc="Label for permission requests, within a list of notification categories. [CHAR-LIMIT=32]">
        Permission requests

components/browser_ui/strings/android/browser_ui_strings.grd

@@ -513,6 +513,9 @@
       <message name="IDS_NOTIFICATION_CATEGORY_DOWNLOADS" desc="Label for notifications shown when something is downloading, within a list of notification categories. [CHAR-LIMIT=32]">
         Active downloads
       </message>
+      <message name="IDS_NOTIFICATION_CATEGORY_MEDIA_PLAYBACK" desc="Label for media playback notifications, within a list of notification categories. [CHAR-LIMIT=32]">
+        Playing media
+      </message>
       <message name="IDS_NOTIFICATION_CATEGORY_WEBRTC_CAM_AND_MIC" desc="Label for notifications shown when media is being recorded from a camera or microphone, within a list of notification categories. [CHAR-LIMIT=32]">
         Camera and microphone use
       </message>

weblayer/browser/java/org/chromium/weblayer_private/WebLayerNotificationChannels.java

@@ -51,12 +51,13 @@ class WebLayerNotificationChannels extends ChannelDefinitions {
      * channel, remove the ID from this StringDef, remove its entry from Predefined Channels.MAP,
      * and add it to the return value of {@link #getLegacyChannelIds()}.
      */
-    @StringDef({ChannelId.ACTIVE_DOWNLOADS, ChannelId.COMPLETED_DOWNLOADS,
+    @StringDef({ChannelId.ACTIVE_DOWNLOADS, ChannelId.COMPLETED_DOWNLOADS, ChannelId.MEDIA_PLAYBACK,
             ChannelId.WEBRTC_CAM_AND_MIC})
     @Retention(RetentionPolicy.SOURCE)
     public @interface ChannelId {
         String ACTIVE_DOWNLOADS = "org.chromium.weblayer.active_downloads";
         String COMPLETED_DOWNLOADS = "org.chromium.weblayer.completed_downloads";
+        String MEDIA_PLAYBACK = "org.chromium.weblayer.media_playback";
         String WEBRTC_CAM_AND_MIC = "org.chromium.weblayer.webrtc_cam_and_mic";
     }
 
@@ -81,6 +82,10 @@ class WebLayerNotificationChannels extends ChannelDefinitions {
                     PredefinedChannel.create(ChannelId.COMPLETED_DOWNLOADS,
                             R.string.notification_category_completed_downloads,
                             NotificationManager.IMPORTANCE_LOW, ChannelGroupId.WEBLAYER));
+            map.put(ChannelId.MEDIA_PLAYBACK,
+                    PredefinedChannel.create(ChannelId.MEDIA_PLAYBACK,
+                            R.string.notification_category_media_playback,
+                            NotificationManager.IMPORTANCE_LOW, ChannelGroupId.WEBLAYER));
             map.put(ChannelId.WEBRTC_CAM_AND_MIC,
                     PredefinedChannel.create(ChannelId.WEBRTC_CAM_AND_MIC,
                             R.string.notification_category_webrtc_cam_and_mic,