C++11: Replace 0 with nullptr where applicable in layout code.

Source/core/layout/compositing/CompositingLayerAssigner.cpp

Index: Source/core/layout/compositing/CompositingLayerAssigner.cpp
diff --git a/Source/core/layout/compositing/CompositingLayerAssigner.cpp b/Source/core/layout/compositing/CompositingLayerAssigner.cpp
index d851ce512e9c100b6c158adbe5e8969c86c5ffb1..ebbe2e4d60c3b8a5107543d89478c8395bf45a1b 100644
--- a/Source/core/layout/compositing/CompositingLayerAssigner.cpp
+++ b/Source/core/layout/compositing/CompositingLayerAssigner.cpp
@@ -210,7 +210,7 @@ void CompositingLayerAssigner::updateSquashingAssignment(DeprecatedPaintLayer* l
             // Before removing |layer| from an already-existing squashing layer that may have other content, issue a paint invalidation.
             m_compositor->paintInvalidationOnCompositingChange(layer);
             layer->groupedMapping()->setNeedsGraphicsLayerUpdate(GraphicsLayerUpdateSubtree);
-            layer->setGroupedMapping(0);
+            layer->setGroupedMapping(nullptr);
         }
 
         // If we need to issue paint invalidations, do so now that we've removed it from a squashed layer.
@@ -241,10 +241,7 @@ void CompositingLayerAssigner::assignLayersToBackingsForReflectionLayer(Deprecat
 static ScrollingCoordinator* scrollingCoordinatorFromLayer(DeprecatedPaintLayer& layer)
 {
     Page* page = layer.layoutObject()->frame()->page();
-    if (!page)
-        return 0;
-
-    return page->scrollingCoordinator();
+    return (!page) ? nullptr : page->scrollingCoordinator();
 }
 
 void CompositingLayerAssigner::assignLayersToBackingsInternal(DeprecatedPaintLayer* layer, SquashingState& squashingState, Vector<DeprecatedPaintLayer*>& layersNeedingPaintInvalidation)
@@ -298,7 +295,7 @@ void CompositingLayerAssigner::assignLayersToBackingsInternal(DeprecatedPaintLay
         layer->scrollParent()->scrollableArea()->setTopmostScrollChild(layer);
 
     if (layer->needsCompositedScrolling())
-        layer->scrollableArea()->setTopmostScrollChild(0);
+        layer->scrollableArea()->setTopmostScrollChild(nullptr);
 
     DeprecatedPaintLayerStackingNodeIterator iterator(*layer->stackingNode(), NormalFlowChildren | PositiveZOrderChildren);
     while (DeprecatedPaintLayerStackingNode* curNode = iterator.next())