GitLab

Since all uses are preceded by IsInt32 checks, it's safe to convert all
these uses to As<v8::Int32> casts.

Bug: v8:7279, v8:8238
Change-Id: I6fadc29adf85294afaa4f7980353ab43add75771
Reviewed-on: https://chromium-review.googlesource.com/c/1349228Reviewed-by: Finnur Thorarinsson <finnur@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610633}