Slimming Paint phase 2 compositing algorithm plumbing & skeleton display list API.

Source/core/layout/compositing/CompositedDeprecatedPaintLayerMapping.cpp

Index: Source/core/layout/compositing/CompositedDeprecatedPaintLayerMapping.cpp
diff --git a/Source/core/layout/compositing/CompositedDeprecatedPaintLayerMapping.cpp b/Source/core/layout/compositing/CompositedDeprecatedPaintLayerMapping.cpp
index 4ed2dcb5e42860baefcf3d5f5cdb9cd6750f03c9..4fced4675ba314dabae510716e0f8df429c27aae 100644
--- a/Source/core/layout/compositing/CompositedDeprecatedPaintLayerMapping.cpp
+++ b/Source/core/layout/compositing/CompositedDeprecatedPaintLayerMapping.cpp
@@ -2082,6 +2082,8 @@ IntRect CompositedDeprecatedPaintLayerMapping::localClipRectForSquashedLayer(con
 void CompositedDeprecatedPaintLayerMapping::doPaintTask(const GraphicsLayerPaintInfo& paintInfo, const PaintLayerFlags& paintLayerFlags, GraphicsContext* context,
     const IntRect& clip) // In the coords of rootLayer.
 {
+    ASSERT(!RuntimeEnabledFeatures::slimmingPaintCompositorLayerizationEnabled() || clip == LayoutRect::infiniteIntRect());
+
     FontCachePurgePreventer fontCachePurgePreventer;
 
     IntSize offset = paintInfo.offsetFromLayoutObject;