Rename the Custom Elements runtime feature to "CustomElements".

Source/core/dom/Document.idl

 /*
  * Copyright (C) 2006, 2007, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006, 2007 Samuel Weinig <sam@webkit.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
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                                                [Default=Undefined] optional long pageX,
                                                [Default=Undefined] optional long pageY,
                                                [Default=Undefined] optional long screenX,
                                                [Default=Undefined] optional long screenY,
                                                [Default=Undefined] optional long webkitRadiusX,
                                                [Default=Undefined] optional long webkitRadiusY,
                                                [Default=Undefined] optional float webkitRotationAngle,
                                                [Default=Undefined] optional float webkitForce);
     [EnabledAtRuntime=touch, Custom, RaisesException] TouchList createTouchList();
 
-    [DeprecateAs=PrefixedDocumentRegister, EnabledAtRuntime=customDOMElements, ImplementedAs=registerElement, CallWith=ScriptState, CustomElementCallbacks=Enable, RaisesException] CustomElementConstructor webkitRegister(DOMString name, optional Dictionary options);
-    [EnabledAtRuntime=customDOMElements, ImplementedAs=registerElement, CallWith=ScriptState, CustomElementCallbacks=Enable, RaisesException] CustomElementConstructor register(DOMString name, optional Dictionary options);
+    [DeprecateAs=PrefixedDocumentRegister, EnabledAtRuntime=customElements, ImplementedAs=registerElement, CallWith=ScriptState, CustomElementCallbacks=Enable, RaisesException] CustomElementConstructor webkitRegister(DOMString name, optional Dictionary options);
+    [EnabledAtRuntime=customElements, ImplementedAs=registerElement, CallWith=ScriptState, CustomElementCallbacks=Enable, RaisesException] CustomElementConstructor register(DOMString name, optional Dictionary options);
     [CustomElementCallbacks=Enable, PerWorldBindings, ActivityLog=AccessForIsolatedWorlds, RaisesException] Element createElement(DOMString localName, [TreatNullAs=NullString] DOMString typeExtension);
     [CustomElementCallbacks=Enable, PerWorldBindings, ActivityLog=AccessForIsolatedWorlds, RaisesException] Element createElementNS([TreatNullAs=NullString] DOMString namespaceURI, DOMString qualifiedName,
                             [TreatNullAs=NullString] DOMString typeExtension);
 
     // Page visibility API.
     readonly attribute DOMString webkitVisibilityState;
     readonly attribute boolean webkitHidden;
 
     // Security Policy API: http://dvcs.w3.org/hg/content-security-policy/raw-file/tip/csp-specification.dev.html#script-interfaces
     [EnabledAtRuntime=experimentalContentSecurityPolicyFeatures] readonly attribute SecurityPolicy securityPolicy;
 
     readonly attribute HTMLScriptElement currentScript;
 };
 
 Document implements ParentNode;