Add CHECK's to debug QuicStreamSequencerBuffer in weird state. Add a destruction indicator to detect free after use.

Also remove some tests because CHECK's prevent some corner case from
happening.

R=rch@chromium.org
BUG=664200

Review-Url: https://codereview.chromium.org/2519333006
Cr-Commit-Position: refs/heads/master@{#434659}
4 files changed