Separate DemuxerHost from DataSourceHost.

This is the first part of work to remove byte range computations out of media::Pipeline, and instead have the DataSource report those directly to Pipeline's parent, which will avoid crossing thread boundaries unnecessarily. This first CL just cleans up the interfaces required to do that, but already eliminates some of the stranger parts of the set-up code.

BUG=122071

Review URL: https://codereview.chromium.org/212803004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@261494 0039d316-1c4b-4281-b951-d872f2087c98
25 files changed