[MSE] http/tests/media/media-source/mediasource-buffered.html is flakey
https://bugs.webkit.org/show_bug.cgi?id=134949

Reviewed by Eric Carlson.

Depending on which SourceBuffer is successfully parsed first, the order of activeSourceBuffers
may change from run to run, breaking the http/tests/media/media-source/mediasource-buffered.html
test. Make the order of activeSourceBuffers the same as (a subset of) sourceBuffers, by replacing
calls to activeSourceBuffers->add() and with a new call to regenerateActiveSourceBuffers(), which
swaps the contents of the SourceBufferList with a new, ordered Vector.

* Modules/mediasource/MediaSource.cpp:
(WebCore::MediaSource::addSourceBuffer):
(WebCore::MediaSource::sourceBufferDidChangeAcitveState):
(WebCore::MediaSource::regenerateActiveSourceBuffers):
* Modules/mediasource/MediaSource.h:
* Modules/mediasource/SourceBufferList.cpp:
(WebCore::SourceBufferList::swap):
* Modules/mediasource/SourceBufferList.h:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@171151 268f45cc-cd09-0410-ab3c-d52691b4dbfc