Heap profiler: add an ability to iterate over snapshot's nodes.

include/v8-profiler.h

Index: include/v8-profiler.h
diff --git a/include/v8-profiler.h b/include/v8-profiler.h
index 940a35c152d7c32398767949af849d807eecb842..dad18a8442db16f3feacf7f7855767833dc2a3d8 100644
--- a/include/v8-profiler.h
+++ b/include/v8-profiler.h
@@ -346,6 +346,12 @@ class V8EXPORT HeapSnapshot {
   /** Returns a node by its id. */
   const HeapGraphNode* GetNodeById(uint64_t id) const;
 
+  /** Returns total nodes count in the snapshot. */
+  int GetNodesCount() const;
+
+  /** Returns a node by index. */
+  const HeapGraphNode* GetNode(int index) const;
+
   /**
    * Deletes the snapshot and removes it from HeapProfiler's list.
    * All pointers to nodes, edges and paths previously returned become