This will simplify the optimizing compiler (no need to pretenure
COW arrays when compiling).

Bug: v8:7790
Change-Id: I7502f43c6b6f7e10bce8536352462731083b5bef
Reviewed-on: https://chromium-review.googlesource.com/1143466Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54566}