The MediaCodecBridge always sets the AAC audio stream as ADTS
(Audio Data Transport Stream). We make MediaCodecAudioDecoder
request ADTS for AAC streams.

This CL adds new method NeedsBitstreamConversion() to the
AudioDecoder interface and uses it in the DecoderStreamTraits.

BUG=542910

Review URL: https://codereview.chromium.org/1708963002

Cr-Commit-Position: refs/heads/master@{#376222}