Track JS allocations as they arrive with no affection on performance when tracking is switched off

src/heap-snapshot-generator.h

Index: src/heap-snapshot-generator.h
diff --git a/src/heap-snapshot-generator.h b/src/heap-snapshot-generator.h
index cea995820f70f5194460b4a813b2082fad7d06b1..7adf925d3c8fcc29ec063a95100c8b9ed34575e8 100644
--- a/src/heap-snapshot-generator.h
+++ b/src/heap-snapshot-generator.h
@@ -225,8 +225,11 @@ class HeapObjectsMap {
 
   void SnapshotGenerationFinished();
   SnapshotObjectId FindEntry(Address addr);
-  SnapshotObjectId FindOrAddEntry(Address addr, unsigned int size);
-  void MoveObject(Address from, Address to);
+  SnapshotObjectId FindOrAddEntry(Address addr,
+                                  unsigned int size,
+                                  bool accessed = true);
+  void MoveObject(Address from, Address to, int size);
+  void NewObject(Address addr, int size);
   SnapshotObjectId last_assigned_id() const {
     return next_id_ - kObjectIdStep;
   }
@@ -245,6 +248,8 @@ class HeapObjectsMap {
   static const SnapshotObjectId kGcRootsFirstSubrootId;
   static const SnapshotObjectId kFirstAvailableObjectId;
 
+  int FindUntrackedObjects();
+
  private:
   struct EntryInfo {
   EntryInfo(SnapshotObjectId id, Address addr, unsigned int size)
@@ -304,12 +309,17 @@ class HeapSnapshotsCollection {
     return ids_.FindOrAddEntry(object_addr, object_size);
   }
   Handle<HeapObject> FindHeapObjectById(SnapshotObjectId id);
-  void ObjectMoveEvent(Address from, Address to) { ids_.MoveObject(from, to); }
+  void ObjectMoveEvent(Address from, Address to, int size) {
+    ids_.MoveObject(from, to, size);
+  }
+  void NewObjectEvent(Address addr, int size) { ids_.NewObject(addr, size); }
   SnapshotObjectId last_assigned_id() const {
     return ids_.last_assigned_id();
   }
   size_t GetUsedMemorySize() const;
 
+  int FindUntrackedObjects() { return ids_.FindUntrackedObjects(); }
+
  private:
   bool is_tracking_objects_;  // Whether tracking object moves is needed.
   List<HeapSnapshot*> snapshots_;