Keep AudioScheduledSourceNode alive until onended is called.

Source/modules/webaudio/AudioBufferSourceNode.idl

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 // A cached (non-streamed), memory-resident audio source
 [
-    Conditional=WEB_AUDIO
+    Conditional=WEB_AUDIO,
+    ActiveDOMObject
 ] interface AudioBufferSourceNode : AudioSourceNode {
     [CustomSetter, SetterRaisesException] attribute AudioBuffer buffer;
 
     const unsigned short UNSCHEDULED_STATE = 0;
     const unsigned short SCHEDULED_STATE = 1;
     const unsigned short PLAYING_STATE = 2;
     const unsigned short FINISHED_STATE = 3;
 
     readonly attribute unsigned short playbackState;
 
     readonly attribute AudioParam gain;
     readonly attribute AudioParam playbackRate;
 
     attribute boolean loop; // This is the proper attribute name from the specification.
 
     attribute double loopStart;
     attribute double loopEnd;
 
     [MeasureAs=WebAudioStart] void start(double when);
     [MeasureAs=WebAudioStart, ImplementedAs=startGrain] void start(double when, double grainOffset);
     [MeasureAs=WebAudioStart, ImplementedAs=startGrain] void start(double when, double grainOffset, double grainDuration);
-    void stop(double when);
+    [ImplementedAs=stopNote] void stop(double when);
 
     [DeprecateAs=WebAudioLooping, ImplementedAs=loop] attribute boolean looping; // This is an alias for the .loop attribute for backwards compatibility.
 
     [MeasureAs=LegacyWebAudio] void noteOn(double when);
     [MeasureAs=LegacyWebAudio] void noteGrainOn(double when, double grainOffset, double grainDuration);
     void noteOff(double when);
 
     attribute EventHandler onended;
 };