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

Source/modules/webaudio/AudioBufferSourceNode.idl

Index: Source/modules/webaudio/AudioBufferSourceNode.idl
diff --git a/Source/modules/webaudio/AudioBufferSourceNode.idl b/Source/modules/webaudio/AudioBufferSourceNode.idl
index c1132b5ea8e4020992f7173042eed22c82923de7..b47eb93b1757f6a7ae4ba72f00a687a4fe2395b2 100644
--- a/Source/modules/webaudio/AudioBufferSourceNode.idl
+++ b/Source/modules/webaudio/AudioBufferSourceNode.idl
@@ -43,14 +43,14 @@
     attribute double loopStart;
     attribute double loopEnd;
 
-    [MeasureAs=WebAudioStart] void start(optional double when, optional double grainOffset, optional double grainDuration);
-    void stop(optional double when);
+    [RaisesException, MeasureAs=WebAudioStart] void start(optional double when, optional double grainOffset, optional double grainDuration);
+    [RaisesException] void stop(optional 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);
+    [RaisesException, ImplementedAs=start, MeasureAs=LegacyWebAudio] void noteOn(double when);
     [MeasureAs=LegacyWebAudio] void noteGrainOn(double when, double grainOffset, double grainDuration);
-    void noteOff(double when);
+    [RaisesException, ImplementedAs=stop] void noteOff(double when);
 
     attribute EventHandler onended;
 };