Adds ChromecastConfig to manage cast_shell's PrefService.

R=lcwu@chromium.org,jam@chromium.org
BUG=336640

Review URL: https://codereview.chromium.org/443833002

Cr-Commit-Position: refs/heads/master@{#288292}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288292 0039d316-1c4b-4281-b951-d872f2087c98
6 files changed