Henry Wilkes authored Apr 13, 2020 and GStreamer Marge Bot committed Apr 29, 2020

Made sure that adding a new track only uses select-tracks-for-object for
core children to determine whether a track elements should be added to the
new track or not, and *not* any other track. In particular, there should
be *no* change in the existing tracks of the timeline when adding another
track. Moreover, a new track should not invoke the creation of track
elements for other tracks.

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