Poor performance of handle leak check

_From [zhao...@google.com](https://code.google.com/u/106321947286816917100/) on November 12, 2013 17:46:11_

The handle leak check cause more than 30sec slowdown

time ~/Workspace/DrMemory/builds/build_x86_drm_dbg.git/bin/drmemory.exe -debug -light -callstack_max_frames 40 -- ./out/Debug/unit_tests.exe --gtest_filter=AutofillDialogControllerTest*

[----------] Global test environment tear-down
[==========] 77 tests from 1 test case ran. (207310 ms total)
[ PASSED ] 77 tests.

real 5m42.338s
user 0m0.016s
sys 0m0.031s

time ~/Workspace/DrMemory/builds/build_x86_drm_dbg.git/bin/drmemory.exe -debug -light -check_handle_leaks -callstack_max_frames 40 -- ./out/Debug/unit_tests.exe --gtest_filter=AutofillDialogControllerTest*

[----------] Global test environment tear-down
[==========] 77 tests from 1 test case ran. (213795 ms total)
[ PASSED ] 77 tests.

real 6m17.887s
user 0m0.015s
sys 0m0.031s

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=1379_