Supporting postMessage from WebAssembly.Module requires implementing
some logic in the ValueSerializer and ValueDeserializer delegates. This
change implements some simple logic for d8.

This change also fixes a DCHECK that occurs when sending a shared
WebAssembly.Memory object to two Workers.

Bug: chromium:857049
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: Idddb23a48175c7175967af3fbc03d8572452a069
Reviewed-on: https://chromium-review.googlesource.com/1117871Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Ben Smith <binji@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54093}