Do the single hash calculation before acquiring the lock, to reduceThis ensures that the last child indexes are calculated in linear time and
lock contention. If Copy is true, and the string was not yet containedcan later be queried in constant time by getLastChild.
The baseline situation was that individual calls to getLastChild were linear in the
in the StringStorage, use the new address from StringStorage,size of DieArray. butCalling getLastChild once for every DWARFDebugInfoEntry was
reuse the hash we already calculatedamortized quadratic in the size of DieArray.