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This is a reland of a692ce8d, I forgot
to update a length test from kMaxStackFrames to kMaxPackedTraceLength in
the original change.

Original change's description:
> GWP-ASan: Pack stack traces to save space
>
> Make use of the stack trace packing from https://crrev.com/627865 to
> reduce memory usage to store stacks on 64-bit systems by ~60% percent. A
> GWP-ASan microbenchmark did not show this change to noticably regress
> performance.
>
> Bug: 896019, 921237
> Change-Id: Iad6e803f18ff12e5fd3079b9821d11bc0918bead
> Reviewed-on: https://chromium-review.googlesource.com/c/1448522
> Auto-Submit: Vlad Tsyrklevich <vtsyrklevich@chromium.org>
> Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
> Reviewed-by: Vitaly Buka <vitalybuka@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#628034}

Bug: 896019, 921237, 927488
Change-Id: I3160735a22e197b18911874e3667504f759552ee
Reviewed-on: https://chromium-review.googlesource.com/c/1449105Reviewed-by: Vitaly Buka <vitalybuka@chromium.org>
Commit-Queue: Vlad Tsyrklevich <vtsyrklevich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628260}