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Record the encryption scheme reported in the video for both the audio and
video streams. Reported when the first AudioDecoderConfig/VideoDecoderConfig
is seen for the file.

BUG=658026
TEST=tested locally

Change-Id: Id210e18f0cedc11800abdce5286eb8488271516a
Reviewed-on: https://chromium-review.googlesource.com/1038784Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Commit-Queue: John Rummell <jrummell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558897}