Clean up code and logic related to platform accessibility node destruction.

ui/accessibility/platform/ax_platform_node_mac.mm

 // Copyright 2014 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.
 
 #import "ui/accessibility/platform/ax_platform_node_mac.h"
 
 #import <Cocoa/Cocoa.h>
 #include <stddef.h>
 
 #include "base/macros.h"
@@ skipping 307 matching lines @@
 
 AXPlatformNodeMac::AXPlatformNodeMac() {
 }
 
 AXPlatformNodeMac::~AXPlatformNodeMac() {
 }
 
 void AXPlatformNodeMac::Destroy() {
   if (native_node_)
     [native_node_ detach];
-  delegate_ = nullptr;
-  delete this;
+  AXPlatformNodeBase::Destroy();
 }
 
 gfx::NativeViewAccessible AXPlatformNodeMac::GetNativeViewAccessible() {
   if (!native_node_)
     native_node_.reset([[AXPlatformNodeCocoa alloc] initWithNode:this]);
   return native_node_.get();
 }
 
 void AXPlatformNodeMac::NotifyAccessibilityEvent(ui::AXEvent event_type) {
   // TODO(dmazzoni): implement this.  http://crbug.com/396137
 }
 
 int AXPlatformNodeMac::GetIndexInParent() {
   // TODO(dmazzoni): implement this.  http://crbug.com/396137
   return -1;
 }
 
 }  // namespace ui