Rework composited scrolling updates.

Source/WebCore/rendering/RenderLayerCompositor.cpp

Index: Source/WebCore/rendering/RenderLayerCompositor.cpp
diff --git a/Source/WebCore/rendering/RenderLayerCompositor.cpp b/Source/WebCore/rendering/RenderLayerCompositor.cpp
index 4d8896984348cdd984a24a978bccf490fcab42e1..7e2ee4af30f6dadcda0788d657c956300f27d81f 100644
--- a/Source/WebCore/rendering/RenderLayerCompositor.cpp
+++ b/Source/WebCore/rendering/RenderLayerCompositor.cpp
@@ -309,6 +309,34 @@ bool RenderLayerCompositor::hasAnyAdditionalCompositedLayers(const RenderLayer*
     return m_compositedLayerCount > (rootLayer->isComposited() ? 1 : 0);
 }
 
+void RenderLayerCompositor::updateDescendantsAreContiguousInStackingOrderRecursive(RenderLayer* layer)
+{
+    for (RenderLayer* child = layer->firstChild(); child; child = child->nextSibling())
+        updateDescendantsAreContiguousInStackingOrderRecursive(child);
+    layer->updateDescendantDependentFlags();
+    layer->updateDescendantsAreContiguousInStackingOrder();
+}
+
+void RenderLayerCompositor::updateNeedsCompositedScrolling(RenderLayer* layer)
+{
+    layer->updateNeedsCompositedScrolling();
+
+    // These values depend on our composited scrolling status.
+    layer->updateIsNormalFlowOnly();
+    layer->updateSelfPaintingLayer();
+
+    for (RenderLayer* child = layer->firstChild(); child; child = child->nextSibling())
+        updateNeedsCompositedScrolling(child);
+}
+
+void RenderLayerCompositor::updateLayoutDependentState()
+{
+    RenderLayer* updateRoot = rootRenderLayer();
+    updateRoot->updateDescendantDependentFlags();
+    updateDescendantsAreContiguousInStackingOrderRecursive(updateRoot);
+    updateNeedsCompositedScrolling(updateRoot);
+}
+
 void RenderLayerCompositor::updateCompositingLayers(CompositingUpdateType updateType, RenderLayer* updateRoot)
 {
     // Avoid updating the layers with old values. Compositing layers will be updated after the layout is finished.