Revert of Introduce SynchronousMutationObserver::didChangeAttribute()

third_party/WebKit/Source/core/dom/SynchronousMutationObserver.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/dom/SynchronousMutationObserver.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/SynchronousMutationNotifier.h"
 
 namespace blink {
 
 SynchronousMutationObserver::SynchronousMutationObserver()
     : LifecycleObserver(nullptr) {}
 
-void SynchronousMutationObserver::didChangeAttribute(const Element&) {}
 void SynchronousMutationObserver::didChangeChildren(const ContainerNode&) {}
 void SynchronousMutationObserver::didMergeTextNodes(const Text&,
                                                     const NodeWithIndex&,
                                                     unsigned) {}
 void SynchronousMutationObserver::didMoveTreeToNewDocument(const Node&) {}
 void SynchronousMutationObserver::didSplitTextNode(const Text&) {}
 void SynchronousMutationObserver::didUpdateCharacterData(CharacterData*,
                                                          unsigned,
                                                          unsigned,
                                                          unsigned) {}
 void SynchronousMutationObserver::nodeChildrenWillBeRemoved(ContainerNode&) {}
 void SynchronousMutationObserver::nodeWillBeRemoved(Node&) {}
 
 }  // namespace blink