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 85%
copy from Source/modules/mediasource/WebKitMediaSource.idl
copy to Source/modules/mediasource/MediaSource.idl
index 573548b1fd2527d0fafdb51debdff885a5e14ba0..188b0810acd168dc343c1172b5afa67722469802 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
@@ -30,22 +30,22 @@
  
 [
     NoInterfaceObject,

[adamk, 2013/06/10 23:05:40]

If you just remove this NoInterfaceObject line, your constructor will
automatically be exposed on the Window object thanks to codegen magic.

[acolwell GONE FROM CHROMIUM, 2013/06/10 23:36:15]

Done.

-    EnabledAtRuntime=webKitMediaSource,
+    EnabledAtRuntime=mediaSource,
     ActiveDOMObject,
     EventTarget,
     Constructor,
     CallWith=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 +62,3 @@
                              optional boolean useCapture);
     [RaisesException] boolean dispatchEvent(Event event);
 };
-