Revert of Fix scroll chaining for non-descendants of root scroller.

third_party/WebKit/Source/core/input/ScrollManager.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/input/ScrollManager.h"
 
 #include "core/dom/DOMNodeIds.h"
 #include "core/events/GestureEvent.h"
 #include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
@@ skipping 65 matching lines @@
     return nullptr;
 }
 
 void ScrollManager::recomputeScrollChain(const Node& startNode,
     std::deque<int>& scrollChain)
 {
     scrollChain.clear();
 
     DCHECK(startNode.layoutObject());
     LayoutBox* curBox = startNode.layoutObject()->enclosingBox();
-    Element* documentElement = m_frame->document()->documentElement();
 
     // Scrolling propagates along the containing block chain and ends at the
     // RootScroller element. The RootScroller element will have a custom
     // applyScroll callback that scrolls the frame or element.
     while (curBox) {
         Node* curNode = curBox->node();
         Element* curElement = nullptr;
 
         // FIXME: this should reject more elements, as part of crbug.com/410974.
         if (curNode && curNode->isElementNode()) {
             curElement = toElement(curNode);
         } else if (curNode && curNode->isDocumentNode()) {
             // In normal circumastances, the documentElement will be the root
             // scroller but the documentElement itself isn't a containing block,
             // that'll be the document node rather than the element.
-            curElement = documentElement;
+            curElement = m_frame->document()->documentElement();
+            DCHECK(!curElement || isEffectiveRootScroller(*curElement));
         }
 
         if (curElement) {
             scrollChain.push_front(DOMNodeIds::idForNode(curElement));
-            if (isEffectiveRootScroller(*curElement)
-                || curElement->isSameNode(documentElement))
+            if (isEffectiveRootScroller(*curElement))
                 break;
         }
 
         curBox = curBox->containingBlock();
     }
 }
 
 bool ScrollManager::logicalScroll(ScrollDirection direction, ScrollGranularity granularity, Node* startNode, Node* mousePressNode)
 {
     Node* node = startNode;
@@ skipping 388 matching lines @@
 DEFINE_TRACE(ScrollManager)
 {
     visitor->trace(m_frame);
     visitor->trace(m_scrollGestureHandlingNode);
     visitor->trace(m_previousGestureScrolledNode);
     visitor->trace(m_scrollbarHandlingScrollGesture);
     visitor->trace(m_resizeScrollableArea);
 }
 
 } // namespace blink