Serialize edge counts instead of indexes in heap snapshot.

src/profile-generator.h

Index: src/profile-generator.h
diff --git a/src/profile-generator.h b/src/profile-generator.h
index 6388985d40a90f08f8ddd77332c22cc55f4ae87d..45dc9a4a44daca80969eb70e7c19b9c7e1a0be84 100644
--- a/src/profile-generator.h
+++ b/src/profile-generator.h
@@ -1072,10 +1072,10 @@ class HeapSnapshotJSONSerializer {
   int GetStringId(const char* s);
   int entry_index(HeapEntry* e) { return e->index() * kNodeFieldsCount; }
   void SerializeEdge(HeapGraphEdge* edge, bool first_edge);
-  void SerializeEdges(const List<HeapEntry>& nodes);
+  void SerializeEdges();
   void SerializeImpl();
-  void SerializeNode(HeapEntry* entry, int edges_index);
-  void SerializeNodes(const List<HeapEntry>& nodes);
+  void SerializeNode(HeapEntry* entry);
+  void SerializeNodes();
   void SerializeSnapshot();
   void SerializeString(const unsigned char* s);
   void SerializeStrings();