Provide windows notifictaion of thread termination

Provide windows notifictaion of thread termination

This code should only have much of an impact on the XP
platform, where thread teardown notification are not
currently made.

Provide an automatic fallback scan of the linker
list of notifcation callbacks via DllMain.

This fallback is ONLY used if there are no notifications
coming via the linker list. This allows all existing
code to continue working as it does today, and provides
thread teardown notifcatino on XP even though we use
the LoadLibrary call.

It is a minimal change, suitable for pushing to other
channels (beta? stable?).

r=cpu
BUG=103209
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=113748

[jar (doing other things), 2011-12-08 07:19:15]

cpu: This is an improved version of the checkin you LGTM'ed Tuesday, which sadly
had a typo (breaking XP in the CHECK() call).

This time I did a "special" try-bot run to verify that it would work when I ran
it on the XP buildbots :-). 

The first upload is exactly what you approved. You can use it to see the changes
in the most recent version.

The last CL upload has the typo CHECK_GT() removed (you can see the delta), and
has more robust logic to be sure the full list of tasks are scanned between the
two "landmarks" I established in dllmain.cc.  

The 2nd-to-last upload is meant to be a try-bot test that will exercise the code
even on non-XP platforms and builds.  That (not to be checked in) nearly-last
upload uses both methods of calling with thread teardown notifications on all
windows platforms.  As a result, the callback code is heavily exercised by the
bots (in contrast with the "real" checkin, which only does anything significant
on XP).

You should see a nice set of green try-bot results on the 2nd-to-last CL... and
that should server as evidence that the CL will do better this time :-/.

[cpu_(ooo_6.6-7.5), 2011-12-08 21:48:34]

lgtm