In the longer run we only want the CBOR code path, for now we need to handle
JSON as well. So we convert if possible.

Change-Id: I726b737f4cd2602d4fb676ce7cf996fcd1ba33e9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1598254Reviewed-by: Alexei Filippov <alph@chromium.org>
Commit-Queue: Johannes Henkel <johannes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61424}