/**
  * Set {@link GroupDelta#putShouldSync(boolean)}, and file internally based on updated state.
  */
 public void setShouldSync(GroupDelta child, boolean shouldSync, boolean attemptRemove) {
   child.putShouldSync(shouldSync);
   if (shouldSync) {
     if (attemptRemove) {
       mUnsyncedGroups.remove(child);
     }
     mSyncedGroups.add(child);
     Collections.sort(mSyncedGroups, sIdComparator);
   } else {
     if (attemptRemove) {
       mSyncedGroups.remove(child);
     }
     mUnsyncedGroups.add(child);
   }
 }