[Android MR] CAF discovery migration

This CL implements/migrates the discovery code to CAF. Also
MediaSource and MediaSink will be shared by caf/ and cast/ so
they are moved to the parent directory.

Bug: 711860
Change-Id: I52bb4d6e4c01bbac60c8361e798af7ee9691429c
Reviewed-on: https://chromium-review.googlesource.com/977564
Commit-Queue: Zhiqiang Zhang <zqzhang@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Thomas Guilbert <tguilbert@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546268}
24 files changed