Bug 1470944 - Don't attempt to create a new demuxer upon changeType call r=bryce

Re-creating a new demuxer is fine, provided that the SourceBufferResource exists. However, a resource is only created upon receiving an init segment.

The segment following a call to changeType() must be an init segment, will let the demuxer creation occurs there.

Differential Revision: https://phabricator.services.mozilla.com/D1812

dom/media/mediasource/TrackBuffersManager.cpp

@@ -286,8 +286,11 @@ TrackBuffersManager::ProcessTasks()
       mType = task->As<ChangeTypeTask>()->mType;
       mChangeTypeReceived = true;
       mInitData = nullptr;
+      // A new input buffer will be created once we receive a new init segment.
+      // The first segment received after a changeType call must be an init
+      // segment.
+      mCurrentInputBuffer = nullptr;
       CompleteResetParserState();
-      CreateDemuxerforMIMEType();
       break;
     default:
       NS_WARNING("Invalid Task");