[MSE][Mac] Adopt new AVStreamDataParser delegate API

[MSE][Mac] Adopt new AVStreamDataParser delegate API
https://bugs.webkit.org/show_bug.cgi?id=127498

Reviewed by Eric Carlson.

Adopt a new delegate API which passes in whether or not the new AVAsset
is discontinuous, implying the AVAsset is entirely new rather than
just updated with new information.

* platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.mm:
(-[WebAVStreamDataParserListener streamDataParser:didParseStreamDataAsAsset:withDiscontinuity:]):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@162630 268f45cc-cd09-0410-ab3c-d52691b4dbfc