Add HW fallback option to software decoding.

Permits falling back to software decoding for unsupported resolutions in
bitstreams.

BUG=4625, chromium:487934
R=mflodman@webrtc.org, stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/46269004

Cr-Original-Commit-Position: refs/heads/master@{#9209}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 7252a2ba8035c4128917a9558a3e34fc9dbe7c44
8 files changed