- Exposes IsSupportedVersion function which compares serialized
  version to current Wasm version.
- Tweaks the comments on serialization to match the code.

Bug: chromium:719172
Change-Id: I76df9605aee16fd98cd82b54dba2e9acbd56b41b
Reviewed-on: https://chromium-review.googlesource.com/c/1265141Reviewed-by: Ben Smith <binji@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56420}