IntersectionObserver: Warn when target is not a descendant of root.

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"
 #include "core/dom/ExceptionCode.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/dom/IntersectionObserverCallback.h"
 #include "core/dom/IntersectionObserverController.h"
 #include "core/dom/IntersectionObserverEntry.h"
 #include "core/dom/IntersectionObserverInit.h"
 #include "core/dom/NodeIntersectionObserverData.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalDOMWindow.h"
 #include "core/frame/LocalFrame.h"
 #include "core/html/HTMLFrameOwnerElement.h"
+#include "core/inspector/ConsoleMessage.h"
 #include "core/layout/LayoutView.h"
 #include "core/timing/DOMWindowPerformance.h"
 #include "core/timing/Performance.h"
 #include "platform/Timer.h"
 #include <algorithm>
 
 namespace blink {
 
 static void parseRootMargin(String rootMarginParameter, Vector<Length>& rootMargin, ExceptionState& exceptionState)
 {
@@ skipping 140 matching lines @@
 
 void IntersectionObserver::observe(Element* target)
 {
     if (!m_root || !target || m_root.get() == target)
         return;
 
     if (target->ensureIntersectionObserverData().getObservationFor(*this))
         return;
 
     bool shouldReportRootBounds = false;
+    bool isDOMDescendant = false;
     LocalFrame* targetFrame = target->document().frame();
-    LocalFrame* rootFrame = rootNode()->document().frame();
-    if (targetFrame && rootFrame)
+    LocalFrame* rootFrame = m_root->document().frame();
+
+    if (target->document() == rootNode()->document()) {
+        shouldReportRootBounds = true;
+        isDOMDescendant = target->isDescendantOf(rootNode());
+    } 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) {
+        m_root->document().addConsoleMessage(ConsoleMessage::create(
+            JSMessageSource, WarningMessageLevel,
+            "IntersectionObserver.observe(target): target element is not a descendant of root."));
+        return;
+    }
+
     if (!rootFrame)
         return;
     if (FrameView* rootFrameView = rootFrame->view())
         rootFrameView->scheduleAnimation();
 }
 
 void IntersectionObserver::unobserve(Element* target)
 {
     if (!target || !target->intersectionObserverData())
         return;
@@ skipping 114 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