Paint local background colors onto foreground layer.

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

Index: third_party/WebKit/Source/core/paint/PaintInfo.h
diff --git a/third_party/WebKit/Source/core/paint/PaintInfo.h b/third_party/WebKit/Source/core/paint/PaintInfo.h
index 8627de1cd49d8b2148a230252800ccd659a91141..2ac32c9eac37ecd18df7ef5f517dc33d8455d581 100644
--- a/third_party/WebKit/Source/core/paint/PaintInfo.h
+++ b/third_party/WebKit/Source/core/paint/PaintInfo.h
@@ -80,6 +80,7 @@ struct CORE_EXPORT PaintInfo {
             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;
     }
 
@@ -110,7 +111,7 @@ 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.