[EME][Mac] Update CDMSessionMediaSourceAVFObjC to match new API provided by AVStreamS...

[EME][Mac] Update CDMSessionMediaSourceAVFObjC to match new API provided by AVStreamSession
https://bugs.webkit.org/show_bug.cgi?id=137469

Reviewed by Brent Fulgham.

Update our forward declaration to match the API provided by AVStreamSession.
AVStreamSession now takes an error: parameter in its initialiazer. It also provides the
sessionIdentifier used by the CDM, which CDMSessionMediaSourceAVFObjC will use as the
value of sessionId. Having this identifier allows us to fire a
secure-proof-of-key-release message after the client calls MediaKeySession.close().
Because this call will now generate messages, which have to be responded to in order
to remove those proofs from storage, do not clear the CDMSession from MediaKeySession
after calling close().

* Modules/encryptedmedia/MediaKeySession.cpp:
(WebCore::MediaKeySession::~MediaKeySession):
(WebCore::MediaKeySession::close):
(WebCore::MediaKeySession::setError): Deleted.
(WebCore::MediaKeySession::sessionId): Deleted.
* platform/graphics/avfoundation/objc/CDMSessionMediaSourceAVFObjC.h:
(WebCore::CDMSessionMediaSourceAVFObjC::setSessionId):
* platform/graphics/avfoundation/objc/CDMSessionMediaSourceAVFObjC.mm:
(-[CDMSessionMediaSourceAVFObjCListener initWithParent:]):
(-[CDMSessionMediaSourceAVFObjCObserver dealloc]):
(-[CDMSessionMediaSourceAVFObjCObserver beginObserving:]):
(-[CDMSessionMediaSourceAVFObjCObserver stopObserving:]):
(-[CDMSessionMediaSourceAVFObjCObserver invalidate]):
(-[CDMSessionMediaSourceAVFObjCListener observeValueForKeyPath:ofObject:change:context:]):
(WebCore::CDMSessionMediaSourceAVFObjC::CDMSessionMediaSourceAVFObjC):
(WebCore::CDMSessionMediaSourceAVFObjC::~CDMSessionMediaSourceAVFObjC):
(WebCore::CDMSessionMediaSourceAVFObjC::releaseKeys):
(WebCore::CDMSessionMediaSourceAVFObjC::update):
(WebCore::CDMSessionMediaSourceAVFObjC::addSourceBuffer):
(WebCore::CDMSessionMediaSourceAVFObjC::removeSourceBuffer):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@174460 268f45cc-cd09-0410-ab3c-d52691b4dbfc