Determine the layoutobject of middleClickAutoscroll by the scroll direction.

third_party/WebKit/Source/core/page/AutoscrollController.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights
  * reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2012 Digia Plc. and/or its subsidiary(-ies)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
@@ skipping 36 matching lines @@
 
 AutoscrollController* AutoscrollController::create(Page& page) {
   return new AutoscrollController(page);
 }
 
 AutoscrollController::AutoscrollController(Page& page)
     : m_page(&page),
       m_autoscrollLayoutObject(nullptr),
       m_pressedLayoutObject(nullptr),
       m_autoscrollType(NoAutoscroll),
-      m_dragAndDropAutoscrollStartTime(0) {}
+      m_dragAndDropAutoscrollStartTime(0),
+      m_middleClickAutoscrolled(false) {}
 
 DEFINE_TRACE(AutoscrollController) {
   visitor->trace(m_page);
 }
 
 bool AutoscrollController::autoscrollInProgress() const {
   return m_autoscrollType == AutoscrollForSelection;
 }
 
 bool AutoscrollController::autoscrollInProgress(
@@ skipping 45 matching lines @@
 void AutoscrollController::stopAutoscrollIfNeeded(LayoutObject* layoutObject) {
   if (m_pressedLayoutObject == layoutObject)
     m_pressedLayoutObject = nullptr;
 
   if (m_autoscrollLayoutObject != layoutObject)
     return;
   m_autoscrollLayoutObject = nullptr;
   m_autoscrollType = NoAutoscroll;
 }
 
+bool AutoscrollController::setMiddleClickAutoscrollLayoutObject(
+    LayoutBox* layoutObject) {
+  if (!m_middleClickAutoscrolled && layoutObject) {
+    m_autoscrollLayoutObject = layoutObject;
+    return true;
+  }
+  return false;
+}
+
 void AutoscrollController::updateAutoscrollLayoutObject() {
   if (!m_autoscrollLayoutObject)
     return;
 
   LayoutObject* layoutObject = m_autoscrollLayoutObject;
 
   if (RuntimeEnabledFeatures::middleClickAutoscrollEnabled()) {
     HitTestResult hitTest =
         layoutObject->frame()->eventHandler().hitTestResultAtPoint(
             m_middleClickAutoscrollStartPos,
@@ skipping 94 matching lines @@
     const IntPoint& lastKnownMousePosition) {
   DCHECK(RuntimeEnabledFeatures::middleClickAutoscrollEnabled());
   // We don't want to trigger the autoscroll or the middleClickAutoscroll if
   // it's already active.
   if (m_autoscrollType != NoAutoscroll)
     return;
 
   m_autoscrollType = AutoscrollForMiddleClick;
   m_autoscrollLayoutObject = scrollable;
   m_middleClickAutoscrollStartPos = lastKnownMousePosition;
+  m_middleClickAutoscrolled = false;
 
   UseCounter::count(m_page->mainFrame(),
                     UseCounter::MiddleClickAutoscrollStart);
   startAutoscroll();
 }
 
 void AutoscrollController::animate(double) {
   if (!m_autoscrollLayoutObject || !m_autoscrollLayoutObject->frame()) {
     stopAutoscroll();
     return;
@@ skipping 82 matching lines @@
   } else if (east) {
     view->setCursor(eastPanningCursor());
   } else if (west) {
     view->setCursor(westPanningCursor());
   } else {
     view->setCursor(middlePanningCursor());
   }
 }
 
 }  // namespace blink