Add an iframe permissions= attribute for implementing permission delegation

third_party/WebKit/Source/core/html/HTMLIFrameElementSandbox.h

 // 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.
 
 #ifndef HTMLIFrameElementSandbox_h
 #define HTMLIFrameElementSandbox_h
 
 #include "core/dom/DOMTokenList.h"
+#include "platform/heap/Handle.h"
 
 namespace blink {
 
-class HTMLIFrameElementSandbox final : public DOMTokenList {
+class HTMLIFrameElement;
+
+class HTMLIFrameElementSandbox final : public DOMTokenList, public DOMTokenListObserver {
+    USING_GARBAGE_COLLECTED_MIXIN(HTMLIFrameElementSandbox);
 public:
-    static HTMLIFrameElementSandbox* create(DOMTokenListObserver* observer = nullptr)
+    static HTMLIFrameElementSandbox* create(HTMLIFrameElement* element)
     {
-        return new HTMLIFrameElementSandbox(observer);
+        return new HTMLIFrameElementSandbox(element);
     }
 
     ~HTMLIFrameElementSandbox() override;
 
+    DECLARE_VIRTUAL_TRACE();
+
 private:
-    explicit HTMLIFrameElementSandbox(DOMTokenListObserver*);
+    explicit HTMLIFrameElementSandbox(HTMLIFrameElement*);
     bool validateTokenValue(const AtomicString&, ExceptionState&) const override;
+
+    // DOMTokenListObserver.
+    void valueWasSet() override;
+
+    Member<HTMLIFrameElement> m_element;
 };
 
 } // namespace blink
 
 #endif