Optimize the pre-paint tree walk and ClipRects

third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp

 // Copyright 2014 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/PaintLayerPainter.h"
 
 #include "core/frame/LocalFrame.h"
 #include "core/layout/LayoutView.h"
 #include "core/paint/ClipPathClipper.h"
 #include "core/paint/FilterPainter.h"
@@ skipping 210 matching lines @@
   // won't cause the paint phases to become non-empty.
   if (paintLayer.needsRepaint())
     needsRepaint = true;
 
   // Repaint if layer's clip changes.
   if (!RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled()) {
     ClipRects& clipRects =
         paintLayer.clipper(PaintLayer::DoNotUseGeometryMapper)
             .paintingClipRects(paintingInfo.rootLayer, respectOverflowClip,
                                subpixelAccumulation);
-    ClipRects* previousClipRects = paintLayer.previousPaintingClipRects();
-    if (&clipRects != previousClipRects &&
-        (!previousClipRects || clipRects != *previousClipRects)) {
+    if (!paintLayer.hasPreviousPaintingClipRects() ||
+        clipRects != paintLayer.previousPaintingClipRects()) {
       needsRepaint = true;
       shouldClearEmptyPaintPhaseFlags = true;
     }
     paintLayer.setPreviousPaintingClipRects(clipRects);
   }
 
   // Repaint if previously the layer might be clipped by paintDirtyRect and
   // paintDirtyRect changes.
   if (paintLayer.previousPaintResult() == MayBeClippedByPaintDirtyRect &&
       paintLayer.previousPaintDirtyRect() != paintingInfo.paintDirtyRect) {
@@ skipping 958 matching lines @@
           context, layoutObject, PaintPhaseClippingMask))
     return;
 
   IntRect snappedClipRect = pixelSnappedIntRect(clipRect.rect());
   LayoutObjectDrawingRecorder drawingRecorder(
       context, layoutObject, PaintPhaseClippingMask, snappedClipRect);
   context.fillRect(snappedClipRect, Color::black);
 }
 
 }  // namespace blink