Clean up packet receive code in media::cast::transport::UdpTransport.

Used iteration to avoid repeated posting of tasks to the IO message loop.

BUG=342578
R=hclam@chromium.org

Review URL: https://codereview.chromium.org/180823002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253701 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253701
[Password Generation] Minor color changes per rolfe@

BUG=318977

Review URL: https://codereview.chromium.org/178223004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253702 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253702