Remove meaningless uses of [TypeChecking=Nullable]

Source/modules/mediasource/SourceBuffer.idl

 /*
  * 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
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 21 matching lines @@
 
 enum AppendMode {
     "segments",
     "sequence"
 };
 
 [
     ActiveDOMObject,
     NoInterfaceObject,
     RuntimeEnabled=MediaSource,
-    TypeChecking=Interface|Nullable|Unrestricted,
+    TypeChecking=Interface|Unrestricted,
 ] interface SourceBuffer : EventTarget {
 
     // Gets or sets the AppendMode.
     // FIXME: Remove MediaSourceExperimental once mode attribute is implemented and stabilized. See http://crbug.com/249422.
     [RaisesException=Setter, RuntimeEnabled=MediaSourceExperimental] attribute AppendMode mode;
 
     readonly attribute boolean updating;
 
     // Returns the time ranges buffered.
     [RaisesException=Getter] readonly attribute TimeRanges buffered;
@@ skipping 13 matching lines @@
 
     [RaisesException, RuntimeEnabled=Stream] void appendStream(Stream stream, optional unsigned long long maxSize);
 
     // Abort the current segment append sequence.
     [RaisesException] void abort();
     // Pending W3C bug: "Change SourceBuffer.remove() end parameter to 'unrestricted double'",
     // https://www.w3.org/Bugs/Public/show_bug.cgi?id=25518
     [RaisesException] void remove(double start, double end);
 };