This patch moves iterator finalization (calling .return() when a
for-of loop exits early) to shipping. The only part of this feature
which is currently known to be missing is destructuring--.return()
should be also be called when destructuring with an array which
does not end in a rest pattern, but it currently does not. The rest
of this feature, including calling .return() from certain builtins,
is implemented.

R=adamk
BUG=v8:3566
LOG=Y

Review URL: https://codereview.chromium.org/1738463003

Cr-Commit-Position: refs/heads/master@{#34307}