Moving Encoder and Decoder to remoting/base

Putting Encder and Decoder together so we can have test that tests both
of them.

TEST=remoting_unittests

Review URL: http://codereview.chromium.org/2840036

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@53427 0039d316-1c4b-4281-b951-d872f2087c98