Reuse cc::PictureLayers when possible for SPv2.

third_party/WebKit/Source/core/paint/PaintInvalidationCapableScrollableArea.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/PaintInvalidationCapableScrollableArea.h"
 
 #include "core/frame/Settings.h"
 #include "core/html/HTMLFrameOwnerElement.h"
 #include "core/layout/LayoutBox.h"
 #include "core/layout/LayoutScrollbar.h"
@@ skipping 10 matching lines @@
     if (!scrollbar.isCustomScrollbar()
         && !(orientation == HorizontalScrollbar ? layerForHorizontalScrollbar() : layerForVerticalScrollbar()))
         ObjectPaintInvalidator(*layoutBox()).slowSetPaintingLayerNeedsRepaintAndInvalidateDisplayItemClient(scrollbar, PaintInvalidationScroll);
 
     ScrollableArea::willRemoveScrollbar(scrollbar, orientation);
 }
 
 static LayoutRect scrollControlPaintInvalidationRect(const IntRect& scrollControlRect, const LayoutBox& box, const PaintInvalidatorContext& context)
 {
     LayoutRect paintInvalidationRect(scrollControlRect);
-    if (!paintInvalidationRect.isEmpty())
+    // No need to apply any paint offset. Scroll controls paint in a different transform space than their contained box
+    // (the scrollbarPaintOffset transform node).
+    if (!paintInvalidationRect.isEmpty() && !RuntimeEnabledFeatures::slimmingPaintV2Enabled())
         context.mapLocalRectToPaintInvalidationBacking(box, paintInvalidationRect);
     return paintInvalidationRect;
 }
 
 // Returns true if the scroll control is invalidated.
 static bool invalidatePaintOfScrollControlIfNeeded(const LayoutRect& newPaintInvalidationRect, const LayoutRect& previousPaintInvalidationRect, bool needsPaintInvalidation, LayoutBox& box, const LayoutBoxModelObject& paintInvalidationContainer)
 {
     bool shouldInvalidateNewRect = needsPaintInvalidation;
     if (newPaintInvalidationRect != previousPaintInvalidationRect) {
         ObjectPaintInvalidator(box).invalidatePaintUsingContainer(paintInvalidationContainer, previousPaintInvalidationRect, PaintInvalidationScroll);
@@ skipping 96 matching lines @@
     fullBounds.unite(m_scrollCornerAndResizerPreviousPaintInvalidationRect);
     return fullBounds;
 }
 
 void PaintInvalidationCapableScrollableArea::scrollControlWasSetNeedsPaintInvalidation()
 {
     layoutBox()->setMayNeedPaintInvalidation();
 }
 
 } // namespace blink