Early out when setting global root scroller

third_party/WebKit/Source/core/page/scrolling/TopDocumentRootScrollerController.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/page/scrolling/TopDocumentRootScrollerController.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/Element.h"
 #include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
@@ skipping 51 matching lines @@
   }
 
   return element;
 }
 
 void TopDocumentRootScrollerController::recomputeGlobalRootScroller() {
   if (!m_viewportApplyScroll)
     return;
 
   Element* target = findGlobalRootScrollerElement();
-  if (!target)
+  if (!target || target == m_globalRootScroller)
     return;
 
   ScrollableArea* targetScroller = RootScrollerUtil::scrollableAreaFor(*target);
 
   if (!targetScroller)
     return;
 
   if (m_globalRootScroller)
     m_globalRootScroller->removeApplyScroll();
 
@@ skipping 94 matching lines @@
   // the root scroller gets composited.
 
   return graphicsLayer;
 }
 
 Element* TopDocumentRootScrollerController::globalRootScroller() const {
   return m_globalRootScroller.get();
 }
 
 }  // namespace blink