Chromecast startup race: don't add filter before HostResolver exists.

HostResolver is on the I/O thread, which doesn't always have a chance
to run before filters are added. Get HostResolver from the I/O thread.

R=lcwu@chromium.org,byungchul@chromium.org
BUG=None, but the internal builders are failing

Review URL: https://codereview.chromium.org/1081673004

Cr-Commit-Position: refs/heads/master@{#326092}
2 files changed