New Heap Profiler: add API method for finding a graph node by id.

include/v8-profiler.h

Index: include/v8-profiler.h
diff --git a/include/v8-profiler.h b/include/v8-profiler.h
index 72195c44f2388803d7dbf9f1c44159d409dd769a..08f47ca36e6346614b8206c80a8cf718f310215b 100644
--- a/include/v8-profiler.h
+++ b/include/v8-profiler.h
@@ -358,6 +358,9 @@ class V8EXPORT HeapSnapshot {
   /** Returns the root node of the heap graph. */
   const HeapGraphNode* GetRoot() const;
 
+  /** Returns a node by its id. */
+  const HeapGraphNode* GetNodeById(uint64_t id) const;
+
   /**
    * Returns a diff between this snapshot and another one. Only snapshots
    * of the same type can be compared.