Pair<Long, NavigableMap<LogSegmentName, Long>> getValidDataSizeByLogSegment(TimeRange timeRange,
      long expiryReferenceTime) throws StoreException {
    return getValidDataSizeByLogSegment(timeRange, expiryReferenceTime, null);
  }
Same as {@link #getValidDataSizeByLogSegment(TimeRange)}, but provides a expiry reference time. Blobs with expiration
time less than the given expiry reference time, are considered as expired.
@param timeRange the delete reference {@link TimeRange} at which the data is requested. Defines both the reference time
                 and the acceptable resolution.
@param expiryReferenceTime the reference time for expired blobs. Blobs with expiration time less than it would be
                           considered as expired. Usually it's now.
@return a {@link Pair} whose first element is the time at which stats was collected (in ms) and whose second
element is the valid data size for each segment in the form of a {@link NavigableMap} of segment names to
valid data sizes.
@throws StoreException
ambry-store/src/main/java/com/github/ambry/store/BlobStoreStats.java