Turn on webaudio for JS backends.

client/dom/generated/src/frog/AudioBufferSourceNode.dart

+
+class AudioBufferSourceNode extends AudioSourceNode native "*AudioBufferSourceNode" {
+
+  AudioBuffer buffer;
+
+  AudioGain gain;
+
+  bool loop;
+
+  bool looping;
+
+  AudioParam playbackRate;
+
+  void noteGrainOn(num when, num grainOffset, num grainDuration) native;
+
+  void noteOff(num when) native;
+
+  void noteOn(num when) native;
+}