Remove inheritance of designMode attribute.

Source/core/dom/Document.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
@@ skipping 785 matching lines @@
     bool execCommand(const String& command, bool showUI, const String& value);
     bool queryCommandEnabled(const String& command);
     bool queryCommandIndeterm(const String& command);
     bool queryCommandState(const String& command);
     bool queryCommandSupported(const String& command);
     String queryCommandValue(const String& command);
 
     KURL openSearchDescriptionURL();
 
     // designMode support
-    enum InheritedBool { off = false, on = true, inherit };
-    void setDesignMode(InheritedBool value);
-    bool inDesignMode() const;
+    bool inDesignMode() const { return m_designMode; }
     String designMode() const;
     void setDesignMode(const String&);
 
     Document* parentDocument() const;
     Document& topDocument() const;
     WeakPtrWillBeRawPtr<Document> contextDocument();
 
     ScriptRunner* scriptRunner() { return m_scriptRunner.get(); }
 
     HTMLScriptElement* currentScript() const { return !m_currentScriptStack.isEmpty() ? m_currentScriptStack.last().get() : nullptr; }
@@ skipping 471 matching lines @@
 
     String m_xmlEncoding;
     String m_xmlVersion;
     unsigned m_xmlStandalone : 2;
     unsigned m_hasXMLDeclaration : 1;
 
     AtomicString m_contentLanguage;
 
     DocumentEncodingData m_encodingData;
 
-    InheritedBool m_designMode;
+    bool m_designMode;
 
     WillBeHeapHashSet<RawPtrWillBeWeakMember<const LiveNodeListBase>> m_listsInvalidatedAtDocument;
 #if ENABLE(OILPAN)
     // Oilpan keeps track of all registered NodeLists.
     //
     // FIXME: Oilpan: improve - only need to know if a NodeList
     // is currently alive or not for the different types.
     HeapHashSet<WeakMember<const LiveNodeListBase>> m_nodeLists[numNodeListInvalidationTypes];
 #else
     unsigned m_nodeListCounts[numNodeListInvalidationTypes];
@@ skipping 128 matching lines @@
 DEFINE_TYPE_CASTS(TreeScope, Document, document, true, true);
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showLiveDocumentInstances();
 #endif
 
 #endif // Document_h