[IntersectionObserver] Enable observations across shadow DOM roots.

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/dom/IntersectionObserver.h"
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "core/css/parser/CSSParserTokenRange.h"
 #include "core/css/parser/CSSTokenizer.h"
 #include "core/dom/Element.h"
@@ skipping 231 matching lines @@
 
     if (target->ensureIntersectionObserverData().getObservationFor(*this))
         return;
     bool shouldReportRootBounds = false;
     bool isDOMDescendant = false;
     LocalFrame* targetFrame = target->document().frame();
     LocalFrame* rootFrame = m_root->document().frame();
 
     if (target->document() == rootNode()->document()) {
         shouldReportRootBounds = true;
-        isDOMDescendant = target->isDescendantOf(rootNode());
+        isDOMDescendant = rootNode()->isShadowIncludingInclusiveAncestorOf(target);
     } else if (targetFrame && rootFrame) {
         shouldReportRootBounds = targetFrame->securityContext()->getSecurityOrigin()->canAccess(rootFrame->securityContext()->getSecurityOrigin());
         isDOMDescendant = (targetFrame->tree().top() == rootFrame);
     }
 
     IntersectionObservation* observation = new IntersectionObservation(*this, *target, shouldReportRootBounds);
     target->ensureIntersectionObserverData().addObservation(*observation);
     m_observations.add(observation);
 
     if (!isDOMDescendant) {
@@ skipping 144 matching lines @@
 
 DEFINE_TRACE(IntersectionObserver)
 {
     visitor->template registerWeakMembers<IntersectionObserver, &IntersectionObserver::clearWeakMembers>(this);
     visitor->trace(m_callback);
     visitor->trace(m_observations);
     visitor->trace(m_entries);
 }
 
 } // namespace blink