[WVDRM] Fix for stuttering on low bandwidth

Reintroduces the play/pause rebuffering logic we eliminated
in JB zero day to fix double spins and slow startup - but
activates that logic only based on a comparison of the
current bandwidth measurement and the lowest bitrate track
in the movie.

Needs to be submitted with related changes in /vendor/widevine

bug: 7230071
Change-Id: If4f5ecda36c4858ce8bf5c4abb722f90a329ecdb