Bug 1398711. P1 - remove unused methods. r=gerald

MozReview-Commit-ID: HHezNUArhVd

--HG--
extra : rebase_source : 4e139d0640dd7335e23332af9d56b88ae499a6e2
extra : intermediate-source : cb1e92dbd1f53874c8d41e36f317c4c5c61bbacf
extra : source : e24555972c08b134654847d950a523c1a836bdb5

dom/media/MediaResource.h

@@ -462,8 +462,6 @@ public:
   void     Suspend(bool aCloseImmediately) override;
   void     Resume() override;
   already_AddRefed<nsIPrincipal> GetCurrentPrincipal() override;
-  // Return true if the stream has been closed.
-  bool     IsClosed() const { return mCacheStream.IsClosed(); }
   bool     CanClone() override;
   already_AddRefed<BaseMediaResource> CloneData(
     MediaResourceCallback* aDecoder) override;