This is in preparation for porting TypedArrayInitialize to CSA.

BUG=v8:5977

Change-Id: I8b4b4bc7a30f3d0dedf85081bb47ec613c7fce52
Reviewed-on: https://chromium-review.googlesource.com/445259
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43364}