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 &page->autoscrollController();
   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 = m_frame->document()->documentElement();
-      DCHECK(!curElement || isEffectiveRootScroller(*curElement));
+      curElement = documentElement;
     }
 
     if (curElement) {
       scrollChain.push_front(DOMNodeIds::idForNode(curElement));
-      if (isEffectiveRootScroller(*curElement))
+      if (isEffectiveRootScroller(*curElement) ||
+          curElement->isSameNode(documentElement))
         break;
     }
 
     curBox = curBox->containingBlock();
   }
 }
 
 bool ScrollManager::logicalScroll(ScrollDirection direction,
                                   ScrollGranularity granularity,
                                   Node* startNode,
@@ skipping 414 matching lines @@
     if (scrollbar->gestureEvent(targetedEvent.event(), &shouldUpdateCapture)) {
       if (shouldUpdateCapture)
         m_scrollbarHandlingScrollGesture = scrollbar;
       return true;
     }
   }
   return false;
 }
 
 }  // namespace blink