NOT FOR REVIEW - Update comp-scrolling state at a well defined point in the pipeline.

Source/core/rendering/RenderLayerCompositor.cpp

Index: Source/core/rendering/RenderLayerCompositor.cpp
diff --git a/Source/core/rendering/RenderLayerCompositor.cpp b/Source/core/rendering/RenderLayerCompositor.cpp
index ad4ee6295990a1ac396be59b0bf122eec013d79c..68948048fa16b19190f95d2683f835836cab75e2 100644
--- a/Source/core/rendering/RenderLayerCompositor.cpp
+++ b/Source/core/rendering/RenderLayerCompositor.cpp
@@ -218,6 +218,8 @@ RenderLayerCompositor::RenderLayerCompositor(RenderView* renderView)
     , m_compositingLayersNeedRebuild(false)
     , m_forceCompositingMode(false)
     , m_inPostLayoutUpdate(false)
+    // PATCH 2
+    , m_needsUpdateCompositingRequirementsState(false)
     , m_isTrackingRepaints(false)
     , m_rootLayerAttachment(RootLayerUnattached)
 #if !LOG_DISABLED
@@ -330,6 +332,46 @@ bool RenderLayerCompositor::hasAnyAdditionalCompositedLayers(const RenderLayer*
     return m_compositedLayerCount > (rootLayer->isComposited() ? 1 : 0);
 }
 
+// PATCH 2
+void RenderLayerCompositor::updateCompositingRequirementsState(CompositingUpdateType updateType, RenderLayer* updateRoot)
+{
+    if (!m_needsUpdateCompositingRequirementsState)
+        return;
+
+    const bool firstIteration = !updateRoot;
+    if (!updateRoot) {
+        bool needsUpdateHasOutOfFlowPositionedDescendant = false;
+        switch (updateType) {
+        case CompositingUpdateAfterStyleChange:
+            needsUpdateHasOutOfFlowPositionedDescendant = true;
+            break;
+        case CompositingUpdateAfterLayout:
+            break;
+        case CompositingUpdateOnScroll:
+        case CompositingUpdateOnCompositedScroll:
+            ASSERT_NOT_REACHED();
+            break;
+        }
+
+        updateRoot = rootRenderLayer();
+        updateRoot->updateDescendantDependentFlags();
+        if (needsUpdateHasOutOfFlowPositionedDescendant) {
+            updateRoot->updateHasOutOfFlowPositionedDescendant();
+        }
+    }
+
+    updateRoot->updateNeedsCompositedScrolling();
+
+    // In this function we update state that determines whether layers are
+    // stacking containers. We may therefore not use this concept here. Instead,
+    // we'll iterate through the tree topologically.
+    for (RenderLayer* child = updateRoot->firstChild(); child; child = child->nextSibling())
+        updateCompositingRequirementsState(updateType, child);
+
+    if (firstIteration)
+        m_needsUpdateCompositingRequirementsState = false;
+}
+
 void RenderLayerCompositor::updateCompositingLayers(CompositingUpdateType updateType, RenderLayer* updateRoot)
 {
     // Avoid updating the layers with old values. Compositing layers will be updated after the layout is finished.