This reduces peak zone memory usage by ~10% on codeload and ~5% on mandreel.

BUG=v8:5209

Committed: https://crrev.com/2648162dcfff622f8587cea2faa8c3af56456968
Review-Url: https://codereview.chromium.org/2209573002
Cr-Original-Commit-Position: refs/heads/master@{#38367}
Cr-Commit-Position: refs/heads/master@{#38390}