DevTools: Fix PostOrder calculation algorithm in heap snapshot.

LayoutTests/inspector/profiler/heap-snapshot-test.js

 var initialize_HeapSnapshotTest = function() {
 
 InspectorTest.createHeapSnapshotMockFactories = function() {
 
 InspectorTest.createJSHeapSnapshotMockObject = function()
 {
     return {
         _rootNodeIndex: 0,
         _nodeTypeOffset: 0,
         _nodeNameOffset: 1,
@@ skipping 42 matching lines @@
 };
 
 InspectorTest.createHeapSnapshotMockRaw = function()
 {
     // Effectively the same graph as in createJSHeapSnapshotMockObject,
     // but having full set of fields.
     //
     // A triple in parentheses indicates node index, self size and
     // retained size.
     //
-    //          --- A (14,2,2) --ac- C (40,4,10) -ce- E(57,6,6)
+    //          --- A (7,2,2) --ac- C (21,4,10) -ce- E(35,6,6)
     //         /    |                /
-    //  "" (1,0,20) 1       --bc-----
+    //  "" (0,0,20) 1       --bc-----
     //         \    v      /
-    //          --- B (27,3,8) --bd- D (50,5,5)
+    //          --- B (14,3,8) --bd- D (28,5,5)
     //
     return {
         snapshot: {
             meta: {
                 node_fields: ["type", "name", "id", "self_size", "retained_size", "dominator", "edge_count"],
                 node_types: [["hidden", "object"], "", "", "", "", "", ""],
                 edge_fields: ["type", "name_or_index", "to_node"],
                 edge_types: [["element", "property", "shortcut"], "", ""]
             },
             node_count: 6,
@@ skipping 648 matching lines @@
         function sortingComplete()
         {
             dataGrid.removeEventListener(WebInspector.HeapSnapshotSortableDataGrid.Events.SortingComplete, sortingComplete, null);
             callback();
         }
         dataGrid.addEventListener(WebInspector.HeapSnapshotSortableDataGrid.Events.SortingComplete, sortingComplete, null);
     }
 };
 
 };