Signal exceptions if start/stop is called out-of-order or too many times.

Source/modules/webaudio/AudioScheduledSourceNode.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 50 matching lines @@
         NotifyEndedTask(PassRefPtr<AudioScheduledSourceNode> scheduledNode);
         void notifyEnded();
 
     private:
         RefPtr<AudioScheduledSourceNode> m_scheduledNode;
     };
 
     AudioScheduledSourceNode(AudioContext*, float sampleRate);
 
     // Scheduling.
-    void start(double when = 0);
-    void stop(double when = 0);
-
-    void noteOn(double when);
-    void noteOff(double when);
+    void start(ExceptionState& es) { start(0.0, es); }
+    void start(double when, ExceptionState&);
+    void stop(ExceptionState& es) { stop(0.0, es); }
+    void stop(double when, ExceptionState&);
 
     unsigned short playbackState() const { return static_cast<unsigned short>(m_playbackState); }
     bool isPlayingOrScheduled() const { return m_playbackState == PLAYING_STATE || m_playbackState == SCHEDULED_STATE; }
     bool hasFinished() const { return m_playbackState == FINISHED_STATE; }
 
     EventListener* onended(DOMWrapperWorld* isolatedWorld) { return getAttributeEventListener(EventTypeNames::ended, isolatedWorld); }
     void setOnended(PassRefPtr<EventListener>, DOMWrapperWorld* isolatedWorld = 0);
 
 protected:
     // Get frame information for the current time quantum.
@@ skipping 17 matching lines @@
 
     // m_startTime is the time to start playing based on the context's timeline (0 or a time less than the context's current time means "now").
     double m_startTime; // in seconds
 
     // m_endTime is the time to stop playing based on the context's timeline (0 or a time less than the context's current time means "now").
     // If it hasn't been set explicitly, then the sound will not stop playing (if looping) or will stop when the end of the AudioBuffer
     // has been reached.
     double m_endTime; // in seconds
 
     bool m_hasEndedListener;
+    bool m_stopCalled;
 
     static const double UnknownTime;
 };
 
 } // namespace WebCore
 
 #endif // AudioScheduledSourceNode_h