Fix scroll chaining for non-descendants of root scroller.

third_party/WebKit/Source/core/input/ScrollManager.cpp

Index: third_party/WebKit/Source/core/input/ScrollManager.cpp
diff --git a/third_party/WebKit/Source/core/input/ScrollManager.cpp b/third_party/WebKit/Source/core/input/ScrollManager.cpp
index d0d2bb9dcbc7db5ce681f1974a7ce32c1c9f3516..e3b5e923f47d6315615e8e1547cb1bb0910c331c 100644
--- a/third_party/WebKit/Source/core/input/ScrollManager.cpp
+++ b/third_party/WebKit/Source/core/input/ScrollManager.cpp
@@ -83,6 +83,7 @@ void ScrollManager::recomputeScrollChain(const Node& startNode,
 
     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
@@ -98,13 +99,13 @@ void ScrollManager::recomputeScrollChain(const Node& startNode,
             // 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;
         }