Bug 1208373 - Don't remove tracks from StreamTracks. Just their content. r=jesup

MozReview-Commit-ID: 6JrnR2IWlAS

--HG--
extra : rebase_source : 9269fa26e6300f14d4a23050b20b07d9de0ecb19
extra : intermediate-source : 95412432bf10a828916936b223f91bc63e60dea8
extra : source : c864d8ec3ba36ead778d798f14b2107a53a6d290

dom/media/StreamTracks.cpp

@@ -103,12 +103,6 @@ StreamTracks::ForgetUpTo(StreamTime aTime)
 
   for (uint32_t i = 0; i < mTracks.Length(); ++i) {
     Track* track = mTracks[i];
-    if (track->IsEnded() && track->GetEnd() <= aTime) {
-      mTracks.RemoveElementAt(i);
-      mTracksDirty = true;
-      --i;
-      continue;
-    }
     StreamTime forgetTo = std::min(track->GetEnd() - 1, aTime);
     track->ForgetUpTo(forgetTo);
   }