Adds ability for tree model to reorder its children. I'm going to use...

chrome/views/tree_model.h

Index: chrome/views/tree_model.h
===================================================================
--- chrome/views/tree_model.h	(revision 10251)
+++ chrome/views/tree_model.h	(working copy)
@@ -39,6 +39,12 @@
                                 int start,
                                 int count) = 0;
 
+  // Notification the children of |parent| have been reordered. Note, only
+  // the direct children of |parent| have been reordered, not descendants.
+  // TODO(sky): make this pure virtual after all sites have been updated.
+  virtual void TreeNodeChildrenReordered(TreeModel* model,
+                                         TreeModelNode* parent) {}
+
   // Notification that the contents of a node has changed.
   virtual void TreeNodeChanged(TreeModel* model, TreeModelNode* node) = 0;
 };