End-to-end prototype of compositor scrolling with slimming paint v2

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.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/paint/PaintPropertyTreeBuilder.h"
 
 #include "core/dom/DOMNodeIds.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
@@ skipping 733 matching lines @@
     PaintPropertyTreeBuilderContext& context) {
   if (object.needsPaintPropertyUpdate() || context.forceSubtreeUpdate) {
     bool needsScrollProperties = false;
     if (object.hasOverflowClip()) {
       auto ancestorReasons =
           context.current.scroll->mainThreadScrollingReasons();
       auto reasons = mainThreadScrollingReasons(object, ancestorReasons);
       bool scrollNodeNeededForMainThreadReasons = ancestorReasons != reasons;
 
       const LayoutBox& box = toLayoutBox(object);
-      const auto* scrollableArea = box.getScrollableArea();
+      auto* scrollableArea = box.getScrollableArea();
       IntSize scrollOffset = box.scrolledContentOffset();
       if (scrollNodeNeededForMainThreadReasons || !scrollOffset.isZero() ||
           scrollableArea->scrollsOverflow()) {
         needsScrollProperties = true;
         auto& properties =
             object.getMutableForPainting().ensurePaintProperties();
 
         IntSize scrollClip = scrollableArea->visibleContentRect().size();
         IntSize scrollBounds = scrollableArea->contentsSize();
         bool userScrollableHorizontal =
@@ skipping 212 matching lines @@
   updateOverflowClip(object, context);
   updatePerspective(object, context);
   updateSvgLocalToBorderBoxTransform(object, context);
   updateScrollAndScrollTranslation(object, context);
   updateOutOfFlowContext(object, context);
 
   context.forceSubtreeUpdate |= object.subtreeNeedsPaintPropertyUpdate();
 }
 
 }  // namespace blink