Revert "Remove incomplete media router API."

This CL has broken all builds on mnc-dev.
Reverting until Jeff can take a look at it.

This reverts commit 2e5a2051de54e64612e1357d4534c7ec851aa508.

Change-Id: Ib9b3569bfebdc7bbfbcb7aee82733b93736c5bb5
6 files changed