IntersectionObserver: use border box rect for unclipped root.

third_party/WebKit/Source/core/dom/IntersectionObservation.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/IntersectionObservation.h"
 
 #include "core/dom/ElementRareData.h"
 #include "core/dom/IntersectionObserver.h"
 #include "core/frame/FrameView.h"
 #include "core/layout/LayoutBox.h"
@@ skipping 37 matching lines @@
     LayoutObject* targetLayoutObject = target()->layoutObject();
     ASSERT(targetLayoutObject && targetLayoutObject->isBoxModelObject());
     rect = toLayoutBoxModelObject(targetLayoutObject)->visualOverflowRect();
 }
 
 void IntersectionObservation::initializeRootRect(LayoutRect& rect) const
 {
     LayoutObject* rootLayoutObject = m_observer->rootLayoutObject();
     if (rootLayoutObject->isLayoutView())
         rect = LayoutRect(toLayoutView(rootLayoutObject)->frameView()->visibleContentRect());
-    // TODO(szager): Obey the spec -- use content box for a scrolling element, border box otherwise.
-    else if (rootLayoutObject->isBox())
+    else if (rootLayoutObject->isBox() && rootLayoutObject->hasOverflowClip())
         rect = LayoutRect(toLayoutBox(rootLayoutObject)->contentBoxRect());
     else
         rect = LayoutRect(toLayoutBoxModelObject(rootLayoutObject)->borderBoundingBox());
     applyRootMargin(rect);
 }
 
 void IntersectionObservation::clipToRoot(IntersectionGeometry& geometry) const
 {
     // Map and clip rect into root element coordinates.
     // TODO(szager): the writing mode flipping needs a test.
@@ skipping 172 matching lines @@
     m_observer.clear();
 }
 
 DEFINE_TRACE(IntersectionObservation)
 {
     visitor->trace(m_observer);
     visitor->trace(m_target);
 }
 
 } // namespace blink