Generate scroll/clip display item hierarchy for SPv2

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 43bb1eabad9834fa3c9196ac1a30caa1d2997265..c43f3b9c130edf22174b6996df0a2cfd9d5052be 100644
--- a/Source/core/layout/compositing/CompositedDeprecatedPaintLayerMapping.cpp
+++ b/Source/core/layout/compositing/CompositedDeprecatedPaintLayerMapping.cpp
@@ -2105,7 +2105,7 @@ void CompositedDeprecatedPaintLayerMapping::doPaintTask(const GraphicsLayerPaint
     IntRect dirtyRect(clip);
     dirtyRect.move(offset);
 
-    if (!(paintLayerFlags & PaintLayerPaintingOverflowContents)) {
+    if (!(paintLayerFlags & PaintLayerPaintingOverflowContents) && !RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {

[chrishtr, 2015/09/17 00:53:46]

Why this change?

[trchen, 2015/09/17 01:56:04]

In rootLayerScrolls-mode the composited bounds will be the size of the viewport
because LayoutView clip and scrolls the document. Our interest rect will
incorrectly cropped in that case.

In normal mode this is no-op.

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

What does this have to do with this CL? 

Furthermore, interest rects will be managed by Blink, not cc, in v2, so all the
code in this file will be obsolete.

         LayoutRect bounds = paintInfo.compositedBounds;
         bounds.move(paintInfo.paintLayer->subpixelAccumulation());
         dirtyRect.intersect(pixelSnappedIntRect(bounds));