This roll includes the SharedArrayBuffer tests (skipping for now)
but doesn't include the $ renaming.

This is a reland; previously, I reverted because I was confused about why
the rename of $ to $262 didn't break tests; it now seems that the
previous patch left it as an alias. This patch does not do the renaming
yet, as the renaming usage has not landed upstream yet.

R=adamk

Review-Url: https://codereview.chromium.org/2685603003
Cr-Commit-Position: refs/heads/master@{#43118}