CRASH in client_malloc_data_free running extension_unittests on Cr MFYI bots

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on September 24, 2014 21:52:48_

one-time: not repeated

at the end: http://build.chromium.org/p/chromium.memory.fyi/builders/Windows%20Unit%20%28DrMemory%29/builds/18803/steps/memory%20test%3A%20extensions/logs/stdio [==========] 656 tests from 90 test cases ran. (310281 ms total)
[ PASSED ] 656 tests.

YOU HAVE 1 DISABLED TEST

% ./symquery -e release/drmemorylib.dll -f -a 0x3791b 0x2ef14
client_malloc_data_free+0x1b
e:\b\build\slave\win-builder\drmemory\drmemory\alloc_drmem.c:399+0x17
replace_free_common+0x1e4
e:\b\build\slave\win-builder\drmemory\common\alloc_replace.c:1873+0x6
% ./symquery -e ../dynamorio/lib32/release/dynamorio.dll -f -a 0xc3dbd
dr_call_on_clean_stack+0x51
E:\b\build\slave\win-builder\build\build_drheapstat-release-32\dynamorio\core\x86.asm_core.s:1286+0x0

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=1639_