Remove UserAgent ShadowRoot + Author ShadowRoot code.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 1883 matching lines @@
     OriginsUsingFeatures::countMainWorldOnly(scriptState, document(), OriginsUsingFeatures::Feature::ElementCreateShadowRoot);
     if (ShadowRoot* root = shadowRoot()) {
         if (root->isV1()) {
             exceptionState.throwDOMException(InvalidStateError, "Shadow root cannot be created on a host which already hosts a v1 shadow tree.");
             return nullptr;
         }
         if (root->type() == ShadowRootType::UserAgent) {
             exceptionState.throwDOMException(InvalidStateError, "Shadow root cannot be created on a host which already hosts an user-agent shadow tree.");
             return nullptr;
         }
+    } else if (alwaysCreateUserAgentShadowRoot()) {
+        exceptionState.throwDOMException(InvalidStateError, "Shadow root cannot be created on a host which already hosts an user-agent shadow tree.");
+        return nullptr;
     }
     document().setShadowCascadeOrder(ShadowCascadeOrder::ShadowCascadeV0);
 
     return createShadowRootInternal(ShadowRootType::V0, exceptionState);
 }
 
 ShadowRoot* Element::attachShadow(const ScriptState* scriptState, const ShadowRootInit& shadowRootInitDict, ExceptionState& exceptionState)
 {
     DCHECK(RuntimeEnabledFeatures::shadowDOMV1Enabled());
 
@@ skipping 1762 matching lines @@
 
 DEFINE_TRACE(Element)
 {
     if (hasRareData())
         visitor->trace(elementRareData());
     visitor->trace(m_elementData);
     ContainerNode::trace(visitor);
 }
 
 } // namespace blink