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..9521c64c2e6bdbfb0d978ce8478ec39a7886490c 100644
--- a/Source/core/rendering/RenderLayerCompositor.cpp
+++ b/Source/core/rendering/RenderLayerCompositor.cpp
@@ -218,6 +218,7 @@ RenderLayerCompositor::RenderLayerCompositor(RenderView* renderView)
     , m_compositingLayersNeedRebuild(false)
     , m_forceCompositingMode(false)
     , m_inPostLayoutUpdate(false)
+    , m_needsUpdateCompositingRequirementsState(false)
     , m_isTrackingRepaints(false)
     , m_rootLayerAttachment(RootLayerUnattached)
 #if !LOG_DISABLED
@@ -330,6 +331,33 @@ bool RenderLayerCompositor::hasAnyAdditionalCompositedLayers(const RenderLayer*
     return m_compositedLayerCount > (rootLayer->isComposited() ? 1 : 0);
 }
 
+void RenderLayerCompositor::updateCompositingRequirementsState(RenderLayer* updateRoot)

[hartmanng, 2013/05/01 20:25:07]

I feel like updateDescendantDependentFlags should be called in here, don't we
need it?

[Ian Vollick, 2013/05/02 03:24:50]

Done.

+{
+    TRACE_EVENT0("blink-rendering", "RenderLayerCompositor::updateCompositingRequirementsState\n");
+
+    if (!m_needsUpdateCompositingRequirementsState)
+        return;
+
+    if (!updateRoot) {
+        updateRoot = rootRenderLayer();
+        updateRoot->updateHasOutOfFlowPositionedDescendant();

[hartmanng, 2013/05/01 20:25:07]

why do we only update this inside the if block?

[Ian Vollick, 2013/05/02 03:24:50]

That call is recursive, so I only want to call it once in the first call to
updateCompositingRequirementsState.

+    }
+
+    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()) {
+#ifndef NDEBUG
+        fprintf(stderr, "vollick: RenderLayerCompositor::updateCompositingRequirementsState\n");
+#endif
+        updateCompositingRequirementsState(child);
+    }
+
+    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.