Rename WebSourceBuffer::abort -> resetParserState

As discussed in https://codereview.chromium.org/1013923002/, we could
rename WebSourceBuffer::abort into WebSourceBuffer::resetParserState to
avoid confusion that it's not the same thing as SourceBuffer::abort, and
just one of the steps of the MSE abort algorithm.

BUG=529497

Review URL: https://codereview.chromium.org/1312763014

Cr-Commit-Position: refs/heads/master@{#348308}
6 files changed