CastContentBrowserClient should not hold CastBrowserMainParts lifetime.

R=lcwu@chromium.org,byungchul@chromium.org
BUG=None

Review URL: https://codereview.chromium.org/463563003

Cr-Commit-Position: refs/heads/master@{#289241}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289241 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed