Enable SiteIsolationExtensions trial for developers.

This CL corrects a typo so that Isolate Extensions is enabled for
developer trunk builds, waterfall bots, perf bots, etc. The goal is
to get broader test coverage and usage of the mode as we turn it on
for Stable users.

This does not affect users who do not receive a field trial config, who still
still have the mode disabled. The mode can also be disabled manually:


Review-Url: https://codereview.chromium.org/2692153002
Cr-Commit-Position: refs/heads/master@{#450821}
5 files changed