Add methods to RenderLayer to get at the painting or scrolling graphics layers, if present.

Source/web/LinkHighlight.cpp

Index: Source/web/LinkHighlight.cpp
diff --git a/Source/web/LinkHighlight.cpp b/Source/web/LinkHighlight.cpp
index 1e1b6010fb92e6b1cdd407e5c4eb460be02a4b9e..765107c03756e74adb7cbcf76d4db8957af234a7 100644
--- a/Source/web/LinkHighlight.cpp
+++ b/Source/web/LinkHighlight.cpp
@@ -122,18 +122,15 @@ RenderLayer* LinkHighlight::computeEnclosingCompositingLayer()
         }
     } while (!renderLayer);
 
-    CompositedLayerMappingPtr compositedLayerMapping = renderLayer->compositingState() == PaintsIntoGroupedBacking ? renderLayer->groupedMapping() : renderLayer->compositedLayerMapping();
-    GraphicsLayer* newGraphicsLayer = renderLayer->compositingState() == PaintsIntoGroupedBacking ? compositedLayerMapping->squashingLayer() : compositedLayerMapping->mainGraphicsLayer();
-
-    m_clipLayer->setTransform(SkMatrix44(SkMatrix44::kIdentity_Constructor));
+    ASSERT(renderLayer->compositingState() != NotComposited);
 
+    GraphicsLayer* newGraphicsLayer = renderLayer->graphicsLayerBacking();
     if (!newGraphicsLayer->drawsContent()) {
-        if (renderLayer->scrollableArea() && renderLayer->scrollableArea()->usesCompositedScrolling()) {
-            ASSERT(renderLayer->hasCompositedLayerMapping() && renderLayer->compositedLayerMapping()->scrollingContentsLayer());
-            newGraphicsLayer = compositedLayerMapping->scrollingContentsLayer();
-        }
+        newGraphicsLayer = renderLayer->graphicsLayerBackingForScrolling();
     }
 
+    m_clipLayer->setTransform(SkMatrix44(SkMatrix44::kIdentity_Constructor));
+
     if (m_currentGraphicsLayer != newGraphicsLayer) {
         if (m_currentGraphicsLayer)
             clearGraphicsLayerLinkHighlightPointer();