port 086d4598 (r32644)

  original commit message:
  The backing store is only held alive indirectly via the array buffer
  referenced by the holder (typed array), so it's not enough to keep the
  elements alive (or even just the external pointer loaded from the
  elements).

BUG=

Review URL: https://codereview.chromium.org/1503943002

Cr-Commit-Position: refs/heads/master@{#32648}