Chromecast media pipeline: handle CENC "full sample encryption" case.

In this case, subsample information is allowed to be elided, but
hardware backends typically translate subsample information into
hardware APIs. To more cleanly map across this, translate this case
into one fully-encrypted "subsample" while transferring DecryptConfigs.,

Review URL:

Cr-Commit-Position: refs/heads/master@{#300123}
1 file changed