RAL: Eliminate n^2 walk to find repaint containers

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index 953e0e3d8e56eb3683396918b6b09c4bc959aba2..bb1f013b85f4a2304f8b39beb421be71e84de2b3 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -1109,6 +1109,11 @@ const RenderLayer* RenderLayer::compositingContainer() const
     return 0;
 }
 
+bool RenderLayer::isRepaintContainer() const
+{
+    return compositingState() == PaintsIntoOwnBacking || compositingState() == PaintsIntoGroupedBacking;

[eseidel, 2014/05/08 00:43:02]

When is this compositing information determined?  During compositing?  Or during
style resolve.  If it's during compositing, then this is making layout dependant
on compositing which is dependent on layout, no?

+}
+
 // FIXME: having two different functions named enclosingCompositingLayer and enclosingCompositingLayerForRepaint
 // is error-prone and misleading for reading code that uses these functions - especially compounded with
 // the includeSelf option. It is very likely that we don't even want either of these functions; A layer
@@ -1133,11 +1138,11 @@ RenderLayer* RenderLayer::enclosingCompositingLayerForRepaint(IncludeSelfOrNot i
 {
     ASSERT(isAllowedToQueryCompositingState());
 
-    if ((includeSelf == IncludeSelf) && (compositingState() == PaintsIntoOwnBacking || compositingState() == PaintsIntoGroupedBacking))
+    if ((includeSelf == IncludeSelf) && isRepaintContainer())
         return const_cast<RenderLayer*>(this);
 
     for (const RenderLayer* curr = compositingContainer(); curr; curr = curr->compositingContainer()) {
-        if (curr->compositingState() == PaintsIntoOwnBacking || curr->compositingState() == PaintsIntoGroupedBacking)
+        if (curr->isRepaintContainer())
             return const_cast<RenderLayer*>(curr);
     }