Determine the layoutobject of middleClickAutoscroll by the scroll direction.

third_party/WebKit/Source/core/dom/Node.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  *
@@ skipping 2153 matching lines @@
       if (enclosingLinkEventParentOrSelf())
         return;
 
       // Avoid that canBeScrolledAndHasScrollableArea changes layout tree
       // structure.
       // FIXME: We should avoid synchronous layout if possible. We can
       // remove this synchronous layout if we avoid synchronous layout in
       // LayoutTextControlSingleLine::scrollHeight
       document().updateStyleAndLayoutIgnorePendingStylesheets();
       LayoutObject* layoutObject = this->layoutObject();
-      while (layoutObject &&
-             (!layoutObject->isBox() ||
-              !toLayoutBox(layoutObject)->canBeScrolledAndHasScrollableArea()))
-        layoutObject = layoutObject->parent();
-
+      while (
+          layoutObject &&
+          (!layoutObject->isBox() ||
+           !toLayoutBox(layoutObject)->canBeScrolledAndHasScrollableArea())) {
+        if (layoutObject->node() && layoutObject->node()->isDocumentNode()) {
+          Element* owner = toDocument(layoutObject->node())->localOwner();
+          layoutObject = owner ? owner->layoutObject() : nullptr;
+        } else {
+          layoutObject = layoutObject->parent();
+        }
+      }
       if (layoutObject) {
         if (LocalFrame* frame = document().frame())
           frame->eventHandler().startMiddleClickAutoscroll(layoutObject);
       }
     }
   } else if (event->type() == EventTypeNames::webkitEditableContentChanged) {
     // TODO(chongz): Remove after shipped.
     // New InputEvent are dispatched in Editor::appliedEditing, etc.
     if (!RuntimeEnabledFeatures::inputEventEnabled())
       dispatchInputEvent();
@@ skipping 300 matching lines @@
   if (node) {
     std::stringstream stream;
     node->printNodePathTo(stream);
     LOG(INFO) << stream.str();
   } else {
     LOG(INFO) << "Cannot showNodePath for <null>";
   }
 }
 
 #endif