Add minimal implementation of unprefixed MediaSource API that has feature parity with prefixed API

Source/modules/mediasource/MediaSource.idl

Index: Source/modules/mediasource/MediaSource.idl
diff --git a/Source/modules/mediasource/WebKitMediaSource.idl b/Source/modules/mediasource/MediaSource.idl
similarity index 84%
copy from Source/modules/mediasource/WebKitMediaSource.idl
copy to Source/modules/mediasource/MediaSource.idl
index 1bc542ccb7d1a7fb7173c466ac936d7ce8aecd70..d0b407dacc56122c130338be2e158733d0269a35 100644
--- a/Source/modules/mediasource/WebKitMediaSource.idl
+++ b/Source/modules/mediasource/MediaSource.idl
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2012 Google Inc. All rights reserved.
+ * Copyright (C) 2013 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
@@ -29,23 +29,22 @@
  */
  
 [
-    NoInterfaceObject,
-    EnabledAtRuntime=webKitMediaSource,
+    EnabledAtRuntime=mediaSource,
     ActiveDOMObject,
     EventTarget,
     Constructor,
     ConstructorCallWith=ScriptExecutionContext
-] interface WebKitMediaSource {
+] interface MediaSource {
     // All the source buffers created by this object.
-    readonly attribute WebKitSourceBufferList sourceBuffers;
+    readonly attribute SourceBufferList sourceBuffers;
 
     // Subset of sourceBuffers that provide data for the selected/enabled tracks.
-    readonly attribute WebKitSourceBufferList activeSourceBuffers;
+    readonly attribute SourceBufferList activeSourceBuffers;
 
     [SetterRaisesException] attribute double duration;
 
-    [RaisesException] WebKitSourceBuffer addSourceBuffer(DOMString type);
-    [RaisesException] void removeSourceBuffer(WebKitSourceBuffer buffer);
+    [RaisesException] SourceBuffer addSourceBuffer(DOMString type);
+    [RaisesException] void removeSourceBuffer(SourceBuffer buffer);
 
     readonly attribute DOMString readyState;
     
@@ -62,4 +61,3 @@
                              optional boolean useCapture);
     [RaisesException] boolean dispatchEvent(Event event);
 };
-