Get rid of a lot of special code for RenderFlowThread invalidation.

Source/web/LinkHighlight.cpp

Index: Source/web/LinkHighlight.cpp
diff --git a/Source/web/LinkHighlight.cpp b/Source/web/LinkHighlight.cpp
index a2ccb01437f7651b34f08a0a06f3139540bedbfc..ae714f288aa77406a5b2b542effe24e7a484bf92 100644
--- a/Source/web/LinkHighlight.cpp
+++ b/Source/web/LinkHighlight.cpp
@@ -107,9 +107,8 @@ void LinkHighlight::releaseResources()
 
 void LinkHighlight::attachLinkHighlightToCompositingLayer(const RenderLayerModelObject* paintInvalidationContainer)
 {
-    // FIXME: there should always be a GraphicsLayer. See https://code.google.com/p/chromium/issues/detail?id=359877.
     GraphicsLayer* newGraphicsLayer = paintInvalidationContainer->layer()->graphicsLayerBacking();
-    if (newGraphicsLayer && !newGraphicsLayer->drawsContent())
+    if (!newGraphicsLayer->drawsContent())
         newGraphicsLayer = paintInvalidationContainer->layer()->graphicsLayerBackingForScrolling();
     if (!newGraphicsLayer)
         return;