Remove stale-while-revalidate from blink

The stale-while-revalidate experiment is being turned down for the
moment. This current implementation is removed due to complexity of
interaction with other existing efforts. See
https://bugs.chromium.org/p/chromium/issues/detail?id=561609#c10.

BUG=348877, 520613, 700568

Review-Url: https://codereview.chromium.org/2767853003
Cr-Commit-Position: refs/heads/master@{#458842}
10 files changed