media: Prefer decrypting pipeline when CDM is attached

In DecoderSelector, if a CDM is attached, always try the decrypting
pipeline first (decoders that support encrypted streams, or decrypting
demuxer stream plus regular decoders), so that the pipeline can handle
encrytped streams later.

BUG=597443
TEST=New tests enabled.

Review-Url: https://codereview.chromium.org/2701203003
Cr-Commit-Position: refs/heads/master@{#452975}
17 files changed