media: Rename EME codec enum names

This is a preparation step before we add AV1 support.

- Remove container from codec enum names.
- EME_CODEC_WEBM_VP9 -> EME_CODEC_LEGACY_VP9 to differentiate from
  EME_CODEC_VP9, which is for the new multi-part VP9.
- DV -> DOLBY_VISION for better readability.

Bug: 884898
Test: No functionality change.
Change-Id: I23117298ca604c0266487c637cacebdfd6884942
Reviewed-on: https://chromium-review.googlesource.com/1240502
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Reviewed-by: John Rummell <jrummell@chromium.org>
Commit-Queue: Xiaohan Wang <xhwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594127}
5 files changed