A previous spec compliance fix for TypedArrays caused a ~4x performance
regression. This patch removes the regression by calling out
to a path within the runtime which implements array copying more
efficiently.

BUG=chromium:592007
R=adamk
LOG=Y

Review URL: https://codereview.chromium.org/1767893002

Cr-Commit-Position: refs/heads/master@{#34601}