Exposing native doubles as doubles when they are read-only or method return values.

sdk/lib/web_audio/dart2js/web_audio_dart2js.dart

Index: sdk/lib/web_audio/dart2js/web_audio_dart2js.dart
diff --git a/sdk/lib/web_audio/dart2js/web_audio_dart2js.dart b/sdk/lib/web_audio/dart2js/web_audio_dart2js.dart
index e0651962137a9b65a67f2abc215df2e4dace743c..3ee1dd5755aaa524975b18b2344bd6fdd60687d6 100644
--- a/sdk/lib/web_audio/dart2js/web_audio_dart2js.dart
+++ b/sdk/lib/web_audio/dart2js/web_audio_dart2js.dart
@@ -74,7 +74,7 @@ class AudioBuffer extends Interceptor native "AudioBuffer" {
 
   @DomName('AudioBuffer.duration')
   @DocsEditable()
-  final num duration;
+  final double duration;
 
   @DomName('AudioBuffer.gain')
   @DocsEditable()
@@ -90,7 +90,7 @@ class AudioBuffer extends Interceptor native "AudioBuffer" {
 
   @DomName('AudioBuffer.sampleRate')
   @DocsEditable()
-  final num sampleRate;
+  final double sampleRate;
 
   @DomName('AudioBuffer.getChannelData')
   @DocsEditable()
@@ -231,7 +231,7 @@ class AudioContext extends EventTarget native "AudioContext" {
 
   @DomName('AudioContext.currentTime')
   @DocsEditable()
-  final num currentTime;
+  final double currentTime;
 
   @DomName('AudioContext.destination')
   @DocsEditable()
@@ -243,7 +243,7 @@ class AudioContext extends EventTarget native "AudioContext" {
 
   @DomName('AudioContext.sampleRate')
   @DocsEditable()
-  final num sampleRate;
+  final double sampleRate;
 
   @DomName('AudioContext.createAnalyser')
   @DocsEditable()
@@ -505,15 +505,15 @@ class AudioParam extends Interceptor native "AudioParam" {
 
   @DomName('AudioParam.defaultValue')
   @DocsEditable()
-  final num defaultValue;
+  final double defaultValue;
 
   @DomName('AudioParam.maxValue')
   @DocsEditable()
-  final num maxValue;
+  final double maxValue;
 
   @DomName('AudioParam.minValue')
   @DocsEditable()
-  final num minValue;
+  final double minValue;
 
   @DomName('AudioParam.name')
   @DocsEditable()