Cast: Get rid of SendPackets in PacketSender.
Next step is to use a callback instead of a PacketSender as
PacketSender is now a single-method interface.

Review URL: https://codereview.chromium.org/143003018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247057 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247057