[Sampling profiler] Define UnwindResult enum and return from Windows stack walk

The result status is not currently used but will be required in order
to integrate with the custom v8 unwinder, to distinguish between
potentially-v8-unwindable state and non-unwindable state.

Bug: 909957
Change-Id: If35fb23be2e86ad4f5543e30f588e4784223fbc8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1529334
Commit-Queue: Mike Wittman <wittman@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Charlie Andrews <charliea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642918}
4 files changed