Revert of Oilpan: Move MediaStreamSource, MediaStreamComponent and MediaStreamDescriptor to oilpan's heap (patchset #5 id:80001 of https://codereview.chromium.org/509933002/)

Reason for revert:
Broke multiple tests in content_unittests.
e.g. https://build.chromium.org/p/chromium.webkit/builders/Linux%20Tests/builds/39151


Original issue's description:
> Oilpan: Move MediaStreamSource, MediaStreamComponent and MediaStreamDescriptor to oilpan's heap
> 
> - MediaStreamSource, MediaStreamComponent and MediaStreamDescriptor must be moved to oilpan's heap in one go because their lifetime are tightly coupled.
> 
> - Removed m_descriptor->setClient(0) from MediaStream's destructor. This is OK because MediaStreamDescriptor has a strong Member back to the Client (i.e., MediaStream).
> 
> - Removed m_component->source()->removeObserver(this) from MediaStreamTrack's destructor. This is OK because this CL made the observers weak (i.e., MediaStreamSource::m_observers is a hash set of weak members to MediaStreamTrack objects).
> 
> - Removed WebMediaStreamTrack::ExtraData::m_owner because it's unused.
> 
> 
> BUG=340522
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=181204

TBR=oilpan-reviews@chromium.org,zerny@chromium.org,haraken@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=340522

Review URL: https://codereview.chromium.org/534473002

git-svn-id: svn://svn.chromium.org/blink/trunk@181207 bbb929c8-8fbe-4397-9dbb-9b2b20218538