Use ByteReader/ByteWriter instead of rtputility and manual shift/add.

BUG=
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/41289004

Cr-Original-Commit-Position: refs/heads/master@{#8761}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 779c3d16b9623f38a72439bc013102aeb0077a62
16 files changed