Change-Id: I916b1e646d9fe142d3483039eb6cc72464529832

Make the base test be:
!(fatal || abort_) removing some redundancy in the encode tests

Change-Id: I8ffaf33fcf9a3030b38ea3e8eb94704cdc2fc920

Change-Id: Id374267c93a7e14e985b8079833364c8eff5248b

The superframe index marker byte carries data in the lower 5 bits. Only the
upper 3 should be used as part of the mask to detect it. By masking with
0xf0, the previous code was incorrect for frames over 65k bytes.

Change-Id: I6248889f5af227457f359a56b2348ef6db87a3b4

A 'superframe' is a group of frames that share the same PTS, but have a
defined decoding order. This commit adds the ability to append an index
to such a group of frames, allowing for random access to the constituent
frames. This could be useful for frame-level parallelism or partial
decoding in a multilayer scenario.

Decoding the stream serially without such an index should work as a
fallback, and VP9/TestSuperframeIndexIsOptional verifies that.

Change-Id: Idff83b7560e1a7077d8fb067bfbc45b567e78b1c