Allow disabling DRP programatically.

Allow disabling DRP programatically if enable-spdy-proxy-auth cmd switch
exists.
Also fixed a bug in DRP auth request handler that didn't set the last
auth_token_invalidation_timestamp_ correctly.

BUG: 17624720

Change-Id: I58013ad7997751a1f4c167f10ed41e54832f2dcd
2 files changed