ok: basic crash handling and stack trace dumps
ok: basic crash handling and stack trace dumps

This seems to work pretty nicely for each engine in the expected case of
few crashes.  The serial and thread engines just dump the first crash
stack to stderr before dying, while the fork engine saves all crashes to
a temporary file, then prints that to stderr once everything's finished.

I'm not sold on this TLS solution as being the best way to know what
was running when we crashed, but it's better than printing nothing.

Change-Id: I0aca66529301b1ad9bd51ec728848817586c606d
Reviewed-on: https://skia-review.googlesource.com/10102
Reviewed-by: Herb Derby <9e12a3d2bbf73546e47cc9958f6ba8f3215b7eaf@google.com>
Commit-Queue: Mike Klein <14574f09dfa9b4e14759b88c3426a495a0e627b0@chromium.org>

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