Chromecast: adds AddKeySystemWithCodecs to key_systems_cast header.

This helper method is also used by internal Chromecast calls.

R=lcwu@chromium.org,byungchul@chromium.org
BUG=400914

Review URL: https://codereview.chromium.org/606483002

Cr-Commit-Position: refs/heads/master@{#296601}
2 files changed