Fix attributes types on AnalyserNode as specification of web audio.

Source/modules/webaudio/AnalyserNode.idl

 /*
  * Copyright (C) 2010, 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 11 matching lines @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 [
     Conditional=WEB_AUDIO
 ] interface AnalyserNode : AudioNode {
     [RaisesException=Setter] attribute unsigned long fftSize;
     readonly attribute unsigned long frequencyBinCount;
 
     // minDecibels / maxDecibels represent the range to scale the FFT analysis data for conversion to unsigned byte values.
-    [RaisesException=Setter] attribute float minDecibels;
-    [RaisesException=Setter] attribute float maxDecibels;
+    [RaisesException=Setter] attribute double minDecibels;
+    [RaisesException=Setter] attribute double maxDecibels;
 
     // A value from 0.0 -> 1.0 where 0.0 represents no time averaging with the last analysis frame.
-    [RaisesException=Setter] attribute float smoothingTimeConstant;
+    [RaisesException=Setter] attribute double smoothingTimeConstant;
 
     // Copies the current frequency data into the passed array.
     // If the array has fewer elements than the frequencyBinCount, the excess elements will be dropped.
     void getFloatFrequencyData(Float32Array array);
     void getByteFrequencyData(Uint8Array array);
 
     // Real-time waveform data
     void getFloatTimeDomainData(Float32Array array);
     void getByteTimeDomainData(Uint8Array array);
 };