Paint local background colors onto foreground layer.

third_party/WebKit/Source/core/paint/PaintInfo.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 62 matching lines @@
 
     // Creates a PaintInfo for painting descendants. See comments about the paint phases
     // in PaintPhase.h for details.
     PaintInfo forDescendants() const
     {
         PaintInfo result(*this);
         if (phase == PaintPhaseDescendantOutlinesOnly)
             result.phase = PaintPhaseOutline;
         else if (phase == PaintPhaseDescendantBlockBackgroundsOnly)
             result.phase = PaintPhaseBlockBackground;
+        result.m_paintFlags &= ~PaintLayerPaintingBackgroundOntoForeground;

[chrishtr, 2016/07/29 21:04:34]

Can you just reuse paintRootBackgroundOnly() instead? That appears to be solving
a similar use case that can be generalized.

[flackr, 2016/08/02 16:58:14]

Done.

[flackr, 2016/08/02 18:37:03]

Hmm, painting with RootBackgroundOnly and then again with SkipRootBackground
seems to be crashing: see failure in
compositing/overflow/overflow-scroll-with-local-background.html. I'm
investigating, will let you know when I find the cause and/or fix it.

         return result;
     }
 
     bool isRenderingClipPathAsMaskImage() const { return m_paintFlags & PaintLayerPaintingRenderingClipPathAsMask; }
 
     bool skipRootBackground() const { return m_paintFlags & PaintLayerPaintingSkipRootBackground; }
     bool paintRootBackgroundOnly() const { return m_paintFlags & PaintLayerPaintingRootBackgroundOnly; }
 
     bool isPrinting() const { return m_globalPaintFlags & GlobalPaintPrinting; }
 
@@ skipping 10 matching lines @@
     void updateCullRect(const AffineTransform& localToParentTransform);
 
     // FIXME: Introduce setters/getters at some point. Requires a lot of changes throughout layout/.
     GraphicsContext& context;
     PaintPhase phase;
 
 private:
     CullRect m_cullRect;
     const LayoutBoxModelObject* m_paintContainer; // the box model object that originates the current painting
 
-    const PaintLayerFlags m_paintFlags;
+    PaintLayerFlags m_paintFlags;
     const GlobalPaintFlags m_globalPaintFlags;
 
     // TODO(chrishtr): temporary while we implement CullRect everywhere.
     friend class SVGPaintContext;
     friend class SVGShapePainter;
 };
 
 } // namespace blink
 
 #endif // PaintInfo_h