Since Mark/Compact also collects garbage in the new space, we can't just
free old space ArrayBuffers during MC - otherwise we run the risk of
never freeing new array buffers

BUG=v8:4201
R=hpayer@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/1199913002

Cr-Commit-Position: refs/heads/master@{#29190}