This pulls the source texts used for the UtfNormalBench.php benchmarks, repeats them into much larger strings, and attempts to reproduce an out-of-memory error in the middle of UtfNormal::cleanUp():
$ php
Testing testdata/washington.txt (English text)...
quickIsNFCVerify 1078.3ms 14,969,652 bytes/s (changed)
cleanUp 992.1ms 16,270,594 bytes/s (no change)
Testing testdata/berlin.txt (German text)...
PHP Fatal error: Allowed memory size of 136314880 bytes exhausted (tried to allocate 71 bytes) in /var/www/trunk/includes/normal/UtfNormal.php on line 285
Exact failure point may require adjustment depending on platform, etc.