[Chromecast] Moves remote debugging start decision into CastContentBrowserClient.

This makes it a runtime decision based on CCBC rather than linking in separate
method definition.

R=halliwell@chromium.org,slan@chromium.org
BUG=None

Review URL: https://codereview.chromium.org/1318393006

Cr-Commit-Position: refs/heads/master@{#348032}
8 files changed