Remove the support of multiple shadow roots with a user agent shadow root

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 1884 matching lines @@
 CustomElementDefinition* Element::customElementDefinition() const
 {
     if (hasRareData())
         return elementRareData()->customElementDefinition();
     return nullptr;
 }
 
 PassRefPtrWillBeRawPtr<ShadowRoot> Element::createShadowRoot(const ScriptState* scriptState, ExceptionState& exceptionState)
 {
     OriginsUsingFeatures::countMainWorldOnly(scriptState, document(), OriginsUsingFeatures::Feature::ElementCreateShadowRoot);
-    ShadowRoot* root = shadowRoot();
-    if (root && (root->type() == ShadowRootType::Open || root->type() == ShadowRootType::Closed)) {
-        exceptionState.throwDOMException(InvalidStateError, "Shadow root cannot be created on a host which already hosts this type of shadow tree.");
-        return nullptr;
+    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;
+        }
     }
     return createShadowRootInternal(ShadowRootType::V0, exceptionState);
 }
 
 PassRefPtrWillBeRawPtr<ShadowRoot> Element::attachShadow(const ScriptState* scriptState, const ShadowRootInit& shadowRootInitDict, ExceptionState& exceptionState)
 {
     ASSERT(RuntimeEnabledFeatures::shadowDOMV1Enabled());
 
     OriginsUsingFeatures::countMainWorldOnly(scriptState, document(), OriginsUsingFeatures::Feature::ElementAttachShadow);
 
@@ skipping 1723 matching lines @@
 {
 #if ENABLE(OILPAN)
     if (hasRareData())
         visitor->trace(elementRareData());
     visitor->trace(m_elementData);
 #endif
     ContainerNode::trace(visitor);
 }
 
 } // namespace blink