Remove document.rootScroller compositing clipping effects.

third_party/WebKit/Source/core/page/scrolling/RootScrollerController.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/RootScrollerController.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/Element.h"
 #include "core/frame/FrameView.h"
 #include "core/layout/LayoutBox.h"
@@ skipping 87 matching lines @@
   // to kick the global root scroller to recompute itself. We can remove this
   // if ScrollCustomization is moved to the Node rather than Element.
   bool oldHasDocumentElement = m_documentHasDocumentElement;
   m_documentHasDocumentElement = m_document->documentElement();
 
   if (oldHasDocumentElement || !m_documentHasDocumentElement) {
     if (m_effectiveRootScroller == newEffectiveRootScroller)
       return;
   }
 
-  PaintLayer* oldRootScrollerLayer = rootScrollerPaintLayer();
-
   m_effectiveRootScroller = newEffectiveRootScroller;
 
-  // This change affects both the old and new layers.
-  if (oldRootScrollerLayer)
-    oldRootScrollerLayer->setNeedsCompositingInputsUpdate();
-  if (rootScrollerPaintLayer())
-    rootScrollerPaintLayer()->setNeedsCompositingInputsUpdate();
-
-  // The above may not be enough as we need to update existing ancestor
-  // GraphicsLayers. This will force us to rebuild the GraphicsLayer tree.
-  if (LayoutView* layoutView = m_document->layoutView()) {
-    layoutView->compositor()->setNeedsCompositingUpdate(
-        CompositingUpdateRebuildTree);
-  }
-
   if (Page* page = m_document->page())
     page->globalRootScrollerController().didChangeRootScroller();
 }
 
 bool RootScrollerController::isValidRootScroller(const Element& element) const {
   if (!element.layoutObject())
     return false;
 
   if (!RootScrollerUtil::scrollableAreaForRootScroller(&element))
     return false;
 
   if (!fillsViewport(element))
     return false;
 
   return true;
 }
 
 PaintLayer* RootScrollerController::rootScrollerPaintLayer() const {
   return RootScrollerUtil::paintLayerForRootScroller(m_effectiveRootScroller);
 }
 
 bool RootScrollerController::scrollsViewport(const Element& element) const {
   if (m_effectiveRootScroller->isDocumentNode())
     return element.isSameNode(m_document->documentElement());
 
   return element.isSameNode(m_effectiveRootScroller);
 }
 
 }  // namespace blink