Generate scroll/clip display item hierarchy for SPv2

Source/core/paint/DeprecatedPaintLayer.cpp

Index: Source/core/paint/DeprecatedPaintLayer.cpp
diff --git a/Source/core/paint/DeprecatedPaintLayer.cpp b/Source/core/paint/DeprecatedPaintLayer.cpp
index a67baee4c4ad558a506e9b5888e7664980a51127..67c6735717339f910182f06766eafae4f4d29803 100644
--- a/Source/core/paint/DeprecatedPaintLayer.cpp
+++ b/Source/core/paint/DeprecatedPaintLayer.cpp
@@ -711,6 +711,18 @@ bool DeprecatedPaintLayer::update3DTransformedDescendantStatus()
     return has3DTransform();
 }
 
+LayoutPoint DeprecatedPaintLayer::locationExcludingOverflowScroll() const
+{
+    ASSERT(RuntimeEnabledFeatures::slimmingPaintV2Enabled());
+
+    // Our m_location already has scroll offset baked-in. We have to revert it here.
+    IntSize scrollOffset;
+    DeprecatedPaintLayer* scrollParent = layoutObject()->isOutOfFlowPositioned() ? enclosingPositionedAncestor() : parent();
+    if (scrollParent && scrollParent->layoutObject()->hasOverflowClip())
+        scrollOffset = scrollParent->layoutBox()->scrolledContentOffset();
+    return m_location + LayoutSize(scrollOffset);
+}
+
 bool DeprecatedPaintLayer::updateLayerPosition()
 {
     LayoutPoint localPoint;
@@ -1244,7 +1256,7 @@ void DeprecatedPaintLayer::insertOnlyThisLayer()
 }
 
 // Returns the layer reached on the walk up towards the ancestor.
-static inline const DeprecatedPaintLayer* accumulateOffsetTowardsAncestor(const DeprecatedPaintLayer* layer, const DeprecatedPaintLayer* ancestorLayer, LayoutPoint& location)
+static inline const DeprecatedPaintLayer* accumulateOffsetTowardsAncestor(const DeprecatedPaintLayer* layer, const DeprecatedPaintLayer* ancestorLayer, LayoutPoint& location, DeprecatedPaintLayer::LocationQueryBehavior behavior)
 {
     ASSERT(ancestorLayer != layer);
 
@@ -1269,10 +1281,10 @@ static inline const DeprecatedPaintLayer* accumulateOffsetTowardsAncestor(const
             // of both relative to the container and subtract.
 
             LayoutPoint thisCoords;
-            layer->convertToLayerCoords(parentLayer, thisCoords);
+            layer->convertToLayerCoords(parentLayer, thisCoords, behavior);
 
             LayoutPoint ancestorCoords;
-            ancestorLayer->convertToLayerCoords(parentLayer, ancestorCoords);
+            ancestorLayer->convertToLayerCoords(parentLayer, ancestorCoords, behavior);
 
             location += (thisCoords - ancestorCoords);
             return ancestorLayer;
@@ -1289,18 +1301,18 @@ static inline const DeprecatedPaintLayer* accumulateOffsetTowardsAncestor(const
     if (!parentLayer)
         return nullptr;
 
-    location += layer->location();
+    location += layer->location(behavior);

[chrishtr, 2015/09/17 18:07:53]

I think this introduces n^2 performance, because of the way that location
without scrolling asks for the positioned ancestor. Instead how about storing
m_locationWithoutScrollOffset directly on each DPL and recomputing along with
m_location?

     return parentLayer;
 }
 
-void DeprecatedPaintLayer::convertToLayerCoords(const DeprecatedPaintLayer* ancestorLayer, LayoutPoint& location) const
+void DeprecatedPaintLayer::convertToLayerCoords(const DeprecatedPaintLayer* ancestorLayer, LayoutPoint& location, LocationQueryBehavior behavior) const
 {
     if (ancestorLayer == this)
         return;
 
     const DeprecatedPaintLayer* currLayer = this;
     while (currLayer && currLayer != ancestorLayer)
-        currLayer = accumulateOffsetTowardsAncestor(currLayer, ancestorLayer, location);
+        currLayer = accumulateOffsetTowardsAncestor(currLayer, ancestorLayer, location, behavior);
 }
 
 void DeprecatedPaintLayer::convertToLayerCoords(const DeprecatedPaintLayer* ancestorLayer, LayoutRect& rect) const