SDK / exoplayer

- It's always fine to prefer the manifest drm init data. In
  DASH we always do this anyway. In SS the manifest and sample
  formats are identical.
- Optimized the case where the manifest and sample formats are
  identical by avoiding the format copy.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=147385282