Make PreParsedScopeData a new array-like instance type, which holds its
child data inline, rather than indirecting to a FixedArray. Should save
one map word per PreParsedScopeData.

TBR=jarin@chromium.org

Bug: chromium:818642
Change-Id: I72dc21160ed9781ad12b18559468f6cce56886fa
Reviewed-on: https://chromium-review.googlesource.com/1127055Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54349}