Remove ShadowDOMV1 runtime flag (status=stable)

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)
  *
@@ skipping 2144 matching lines @@
     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());
-
   HostsUsingFeatures::countMainWorldOnly(
       scriptState, document(),
       HostsUsingFeatures::Feature::ElementAttachShadow);
 
   const AtomicString& tagName = localName();
   bool tagNameIsSupported =
       isV0CustomElement() ||
       getCustomElementState() != CustomElementState::Uncustomized ||
       tagName == HTMLNames::articleTag || tagName == HTMLNames::asideTag ||
       tagName == HTMLNames::blockquoteTag || tagName == HTMLNames::bodyTag ||
@@ skipping 1912 matching lines @@
 }
 
 DEFINE_TRACE_WRAPPERS(Element) {
   if (hasRareData()) {
     visitor->traceWrappers(elementRareData());
   }
   ContainerNode::traceWrappers(visitor);
 }
 
 }  // namespace blink