along with follow-up fixes:

- "introduce LookupIterator::Restart() and use it"
- "always reset the LookupIterator before storing"
- "API-style accessors can throw, check for that"

Revert reason was fixed in Chromium: https://codereview.chromium.org/1415453003/

This reverts the following commits:
0188aead
984f8af8
dc9d2c16
a0f5d499

Review URL: https://codereview.chromium.org/1424503003

Cr-Commit-Position: refs/heads/master@{#31578}