Drop [LegacyInterfaceTypeChecking] where trivial in core/

third_party/WebKit/Source/core/dom/MutationObserver.idl

 /*
  * Copyright (C) 2011 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 17 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 // https://dom.spec.whatwg.org/#interface-mutationobserver
 
 [
     CustomConstructor(MutationCallback callback),
     Custom=VisitDOMWrapper,
     WillBeGarbageCollected,
 ] interface MutationObserver {
-    [RaisesException, LegacyInterfaceTypeChecking] void observe(Node target, MutationObserverInit options);
+    [RaisesException] void observe(Node target, MutationObserverInit options);
     void disconnect();
     sequence<MutationRecord> takeRecords();
 };