A bytecode array can be serialized while concurrent marking is running
and aging the bytecode array, which results in a data race.

This patch ensures that the age byte of a bytecode array is not
accessed during serialization.

Bug: v8:7085
Change-Id: I83e4b67fbef0754bf75015b4d1b9b660a0cd402f
Reviewed-on: https://chromium-review.googlesource.com/785677
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49612}