Avoid tree walks when computing RenderLayer::scrollParent

Source/core/rendering/compositing/RenderLayerCompositor.cpp

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 370 matching lines @@
         m_pendingUpdateType = GraphicsLayerUpdater::ForceUpdate;
         break;
     case CompositingUpdateAfterCanvasContextChange:
         m_needsToUpdateLayerTreeGeometry = true;
         break;
     }
 
     m_renderView.frameView()->scheduleAnimation();
 }
 
+static void clearAncestorDependentPropertyCacheRecursive(RenderLayer* layer)
+{
+    layer->clearAncestorDependentPropertyCache();
+    RenderLayerStackingNodeIterator iterator(*layer->stackingNode(), AllChildren);
+    for (RenderLayer* child = layer->firstChild(); child; child = child->nextSibling())
+        clearAncestorDependentPropertyCacheRecursive(child);
+}
+
 void RenderLayerCompositor::updateCompositingLayers()
 {
     TRACE_EVENT0("blink_rendering", "RenderLayerCompositor::updateCompositingLayers");
 
     // FIXME: We should carefully clean up the awkward early-exit semantics, balancing
     // between skipping unnecessary compositing updates and not incorrectly skipping
     // necessary updates.
 
     // Avoid updating the layers with old values. Compositing layers will be updated after the layout is finished.
     // FIXME: Can we assert that we never return here?
     if (m_renderView.needsLayout())
         return;
 
     lifecycle().advanceTo(DocumentLifecycle::InCompositingUpdate);
 
     updateCompositingLayersInternal();
 
+    // Clear data only valid during compositing updates.
+    clearAncestorDependentPropertyCacheRecursive(rootRenderLayer());
+
     lifecycle().advanceTo(DocumentLifecycle::CompositingClean);
 
     DocumentAnimations::startPendingAnimations(m_renderView.document());
     ASSERT(m_renderView.document().lifecycle().state() == DocumentLifecycle::CompositingClean);
 }
 
 void RenderLayerCompositor::updateCompositingLayersInternal()
 {
     if (isMainFrame() && m_renderView.frameView())
         finishCompositingUpdateForFrameTree(&m_renderView.frameView()->frame());
@@ skipping 1822 matching lines @@
     } else if (graphicsLayer == m_scrollLayer.get()) {
         name = "LocalFrame Scrolling Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore