Cast: Fix cast sender app crashes.

- Add CommandLine::Init() to sender.cc
- CastTransportSender should use cast_environment->Clock() instead of
  clock.get() as the latter is null after Pass() to cast_environment

BUG=

Review URL: https://codereview.chromium.org/192893006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256142 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256142