The next Fuchsia SDK roll changes the signature and types associated
with the zx_thread_read_state() API, so we temporarily need backward-
compatibility shims while we roll the SDK/Chromium/V8.

Bug: chromium:707030
Change-Id: I419a65bbb631a1ef0d7d5044b07d4cbbac08970f
Reviewed-on: https://chromium-review.googlesource.com/914695
Commit-Queue: Wez <wez@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51256}