This doesn't change the API, it just makes it functional: the
functions were declared already, but they lacked an implementation
so far. Trying to use them in Blink detects that issue.

Bug: v8:6791
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I48902a5bba4a42f2922eafd22858d584731fc777
Reviewed-on: https://chromium-review.googlesource.com/1014668Reviewed-by: Daniel Clifford <danno@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52632}