Enable tcmalloc validation by default in debug builds

Enable tcmalloc validation by default in debug builds

BUG=none
TEST=


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=102083

[jamesr, 2011-09-20 19:51:11]

This enables some tcmalloc validation logic (that I believe you wrote) by
default in debug.  The part that I've found particularly useful is the filling
of freed memory with an 0x36 pattern - that's been extremely helpful in
diagnosing and debugging use after frees.

I've been running with this change locally for the past month or so, primarily
chrome itself and layout tests, without any trouble.  I also submitting this to
every try bot I could find that runs windows/linux/chromeos (since we don't use
tcmalloc on mac).  I expect this to have a performance impact for debug builds
but don't think that is significant.

[jar (doing other things), 2011-09-20 23:29:58]

LGTM

Thanks for suggesting this!!

Justin/Bxx:

I think the "scribbbling" this does will not be validated, and is done just
before pushing things onto the free list, and just after taking it off.  As a
result, it won't interfere with the doubly linked list implementation.

Tthis is only for DEBUG builds, and hence not really a security implementation
(it is expensive because it adds an adjacent tag to each allocated block, and it
also in debug spends time zapping memory during allocation and free).

[commit-bot: I haz the power, 2011-09-21 03:51:07]

Change committed as 102083