Update notification blocking documentation.

Change-Id: I3e5425321d127fbf11adfa1c4ac5bed53fc73e03
Fixes: 73750866
Test: make

core/java/android/app/NotificationChannel.java

@@ -463,7 +463,11 @@ public final class NotificationChannel implements Parcelable {
 
     /**
      * Returns the user specified importance e.g. {@link NotificationManager#IMPORTANCE_LOW} for
-     * notifications posted to this channel.
+     * notifications posted to this channel. Note: This value might be >
+     * {@link NotificationManager#IMPORTANCE_NONE}, but notifications posted to this channel will
+     * not be shown to the user if the parent {@link NotificationChannelGroup} or app is blocked.
+     * See {@link NotificationChannelGroup#isBlocked()} and
+     * {@link NotificationManager#areNotificationsEnabled()}.
      */
     public int getImportance() {
         return mImportance;

core/java/android/app/NotificationChannelGroup.java

@@ -145,7 +145,9 @@ public final class NotificationChannelGroup implements Parcelable {
 
     /**
      * Returns whether or not notifications posted to {@link NotificationChannel channels} belonging
-     * to this group are blocked.
+     * to this group are blocked. This value is independent of
+     * {@link NotificationManager#areNotificationsEnabled()} and
+     * {@link NotificationChannel#getImportance()}.
      */
     public boolean isBlocked() {
         return mBlocked;