spyglass/src/main/java/com/linkedin/android/spyglass/ui/MentionsEditText.java
@SuppressWarnings("unused")
    public void addMentionWatcher(@NonNull MentionWatcher watcher) {
        if (!mMentionWatchers.contains(watcher)) {
            mMentionWatchers.add(watcher);
        }
    }
@SuppressWarnings("unused")
    public void addMentionWatcher(@NonNull MentionWatcher watcher) {
        if (!mMentionWatchers.contains(watcher)) {
            mMentionWatchers.add(watcher);
        }
    }
Register a {@link com.linkedin.android.spyglass.ui.MentionsEditText.MentionWatcher} in order to receive callbacks
when mentions are changed.

@param watcher the {@link com.linkedin.android.spyglass.ui.MentionsEditText.MentionWatcher} to add