Early out when setting global root scroller

third_party/WebKit/Source/core/frame/RootFrameViewport.cpp

 // Copyright 2015 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/frame/RootFrameViewport.h"
 
 #include "core/frame/FrameView.h"
 #include "core/layout/ScrollAlignment.h"
 #include "core/layout/ScrollAnchor.h"
 #include "platform/geometry/DoubleRect.h"
 #include "platform/geometry/FloatRect.h"
 #include "platform/geometry/LayoutRect.h"
 
 namespace blink {
 
 RootFrameViewport::RootFrameViewport(ScrollableArea& visualViewport,
                                      ScrollableArea& layoutViewport)
     : m_visualViewport(visualViewport) {
   setLayoutViewport(layoutViewport);
 }
 
 void RootFrameViewport::setLayoutViewport(ScrollableArea& newLayoutViewport) {
+  if (m_layoutViewport.get() == &newLayoutViewport)
+    return;
+
   if (m_layoutViewport && m_layoutViewport->scrollAnchor())
     m_layoutViewport->scrollAnchor()->setScroller(m_layoutViewport.get());
 
   m_layoutViewport = &newLayoutViewport;
 
   if (m_layoutViewport->scrollAnchor())
     m_layoutViewport->scrollAnchor()->setScroller(this);
 }
 
 ScrollableArea& RootFrameViewport::layoutViewport() const {
@@ skipping 391 matching lines @@
   visualViewport().clearScrollAnimators();
 }
 
 DEFINE_TRACE(RootFrameViewport) {
   visitor->trace(m_visualViewport);
   visitor->trace(m_layoutViewport);
   ScrollableArea::trace(visitor);
 }
 
 }  // namespace blink