GitLab

Interfaces only at this point.  Implementation to follow.  API mirrors
that which is provided to the CDMs in http://crrev.com/221019

CanChallengePlatform() can be synchronous since it will just check a
command line flag passed to the process.

BUG=270294
TEST=none
R=ddorwin@chromium.org, dmichael@chromium.org

Review URL: https://codereview.chromium.org/23569005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@222113 0039d316-1c4b-4281-b951-d872f2087c98