code: public Map<String, Integer> getOnTierPercentages() {
      return mOrderedTierAliases.stream().collect(Collectors.toMap(tier -> tier, tier -> {
        Long sizeOnTier = mSizeOnTier.getOrDefault(tier, 0L);
        return mSize > 0 ? (int) (100 * sizeOnTier / mSize) : 0;
      }));
    }
docs: Gets on-tier percentages.
  
  @return the on-tier percentages