This adds a new API function and provides a simple implementation
of performance.measureMemory() in d8. The implementation currently
immediately resolves the result promise with the current heap size.

Bug: chromium:973627

Change-Id: Ia8e1963a49b7df628b5487a2c0d601473f0cb039
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1796502
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63694}