Fix object ownership in ui/base/models.

ui/base/models/tree_node_iterator.h

Index: ui/base/models/tree_node_iterator.h
diff --git a/ui/base/models/tree_node_iterator.h b/ui/base/models/tree_node_iterator.h
index 3a80e7c89c3da876c47929001f07afcaad6d6279..e383a2da3fc194fb82239a92825b04fb94c62555 100644
--- a/ui/base/models/tree_node_iterator.h
+++ b/ui/base/models/tree_node_iterator.h
@@ -25,7 +25,7 @@ class TreeNodeIterator {
  public:
   typedef base::Callback<bool(NodeType*)> PruneCallback;
 
-  // This contructor accepts an optional filter function |prune| which could be
+  // This constructor accepts an optional filter function |prune| which could be
   // used to prune complete branches of the tree. The filter function will be
   // evaluated on each tree node and if it evaluates to true the node and all
   // its descendants will be skipped by the iterator.
@@ -57,7 +57,7 @@ class TreeNodeIterator {
   NodeType* Next() {
     if (!has_next()) {
       NOTREACHED();
-      return NULL;
+      return nullptr;
     }
 
     // There must always be a valid node in the current Position index.
@@ -90,7 +90,7 @@ class TreeNodeIterator {
   template <class PositionNodeType>
   struct Position {
     Position(PositionNodeType* node, int index) : node(node), index(index) {}
-    Position() : node(NULL), index(-1) {}
+    Position() : node(nullptr), index(-1) {}
 
     PositionNodeType* node;
     int index;