Rename SBR::IsNextInSequence

We'll need an additional IsNextInPresentationSequence method as part of
PTS/DTS compliance. This change renames the existing method to
IsNextInDecodeSequence, adds comments, moves the implementation of the
method to align with declaration order in the header, and adds a
CHECK(!buffers_.empty()) precondition check.

BUG=718641
R=chcunningham@chromium.org

Change-Id: Idb44cb85a7821ef6d37a7e677c8e03729aa732bb
Reviewed-on: https://chromium-review.googlesource.com/526372
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Commit-Queue: Matthew Wolenetz <wolenetz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#477403}
2 files changed