MediaRouter: Disable transcriptMode when it's not animating

transcriptMode was used to show the last item first on expand animation.
But, it led to an unexpected behavior when the user change the volume.
This change disables it if it's not animating.

Bug: 24555909
Change-Id: I5fc4fb89191e0fe4da856ede53a09fb0e1ad9236
2 files changed