Early out when setting global root scroller

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

Index: third_party/WebKit/Source/core/frame/RootFrameViewport.cpp
diff --git a/third_party/WebKit/Source/core/frame/RootFrameViewport.cpp b/third_party/WebKit/Source/core/frame/RootFrameViewport.cpp
index 509cc8627efd3f1f5cdfacd2f5610235bb648734..5bcea2be9e95fcec89ed48dc732d1102b5d26fb2 100644
--- a/third_party/WebKit/Source/core/frame/RootFrameViewport.cpp
+++ b/third_party/WebKit/Source/core/frame/RootFrameViewport.cpp
@@ -20,6 +20,9 @@ RootFrameViewport::RootFrameViewport(ScrollableArea& visualViewport,
 }
 
 void RootFrameViewport::setLayoutViewport(ScrollableArea& newLayoutViewport) {
+  if (m_layoutViewport.get() == &newLayoutViewport)
+    return;
+
   if (m_layoutViewport && m_layoutViewport->scrollAnchor())
     m_layoutViewport->scrollAnchor()->setScroller(m_layoutViewport.get());