Revert 162886 "MediaStream API: MediaStreamTrack can now belong ..."

> MediaStream API: MediaStreamTrack can now belong to more than one Stream.
> MediaStream::addTrack now adds the track directly instead of cloning it
> first.
> 
> This patch has already been committed as r162758, rolled back due to a
> failing browsertest in r162808. The failing browsertest has been slightly
> changed to cope with both the old and new behaviour, and this patch have
> had one line changed to correct another found issue.
> 
> BUG=294145
> 
> Review URL: https://codereview.chromium.org/95183003

TBR=tommyw@chromium.org

Review URL: https://codereview.chromium.org/98403008

git-svn-id: svn://svn.chromium.org/blink/trunk@163364 bbb929c8-8fbe-4397-9dbb-9b2b20218538