{Video|Audio}TrackConfiguration should be a dictionary

Partially address Issue WebKit#98 by making the configuration objects `dictionary` types rather than `interfaces.

TrackConfiguration/README.md

@@ -33,20 +33,20 @@ A page would like to validate that its encoder and muxer generates media whose `
 The `HTMLMediaElement`’s `VideoTrack` and `AudioTrack` objects would vend a new attribute `VideoTrackConfiguration` and `AudioTrackConfiguration`. 
 
 ```
-interface VideoTrackConfiguration {
-    readonly attribute DOMString codec;
-    readonly attribute unsigned long long bitrate;
-    readonly attribute double framerate;
-    readonly attribute unsigned long width;
-    readonly attribute unsigned long height;
-    readonly attribute VideoColorSpace colorSpace;
+dictionary VideoTrackConfiguration {
+    attribute DOMString codec;
+    attribute unsigned long long bitrate;
+    attribute double framerate;
+    attribute unsigned long width;
+    attribute unsigned long height;
+    attribute VideoColorSpace colorSpace;
 };
 
-interface AudioTrackConfiguration {
-    readonly attribute DOMString codec;
-    readonly attribute unsigned long long bitrate;
-    readonly attribute unsigned long sampleRate;
-    readonly attribute unsigned long numberOfChannels;
+dictionary AudioTrackConfiguration {
+    attribute DOMString codec;
+    attribute unsigned long long bitrate;
+    attribute unsigned long sampleRate;
+    attribute unsigned long numberOfChannels;
 };
 
 partial interface VideoTrack {