Use memmove if source and target are either Uint8Array or Uint8ClampedArray.

Bug: v8:7123,chromium:759236
Change-Id: If82bf10165cfc67274f36bb772ce9676a768dcc8
Reviewed-on: https://chromium-review.googlesource.com/790756
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49678}