Add HeapProfiler::GetPersistentHandleCount to be able to track the number of persistent handles

src/global-handles.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 125 matching lines @@
   int NumberOfWeakHandles() { return number_of_weak_handles_; }
 
   void RecordStats(HeapStats* stats);
 
   // Returns the current number of weak handles to global objects.
   // These handles are also included in NumberOfWeakHandles().
   int NumberOfGlobalObjectWeakHandles() {
     return number_of_global_object_weak_handles_;
   }
 
+  // Returns the current number of handles to global objects.
+  int NumberOfGlobalHandles() {
+    return number_of_global_handles_;
+  }
+
   // Clear the weakness of a global handle.
   void ClearWeakness(Object** location);
 
   // Clear the weakness of a global handle.
   void MarkIndependent(Object** location);
 
   // Tells whether global handle is near death.
   static bool IsNearDeath(Object** location);
 
   // Tells whether global handle is weak.
@@ skipping 85 matching lines @@
   Isolate* isolate_;
 
   // Field always containing the number of weak and near-death handles.
   int number_of_weak_handles_;
 
   // Field always containing the number of weak and near-death handles
   // to global objects.  These objects are also included in
   // number_of_weak_handles_.
   int number_of_global_object_weak_handles_;
 
+  // Field always containing the number of handles to global objects.
+  int number_of_global_handles_;
+
   // List of all allocated node blocks.
   NodeBlock* first_block_;
 
   // List of node blocks with used nodes.
   NodeBlock* first_used_block_;
 
   // Free list of nodes.
   Node* first_free_;
 
   // Contains all nodes holding new space objects. Note: when the list
   // is accessed, some of the objects may have been promoted already.
   List<Node*> new_space_nodes_;
 
   int post_gc_processing_count_;
 
   List<ObjectGroup*> object_groups_;
   List<ImplicitRefGroup*> implicit_ref_groups_;
 
   friend class Isolate;
 
   DISALLOW_COPY_AND_ASSIGN(GlobalHandles);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_GLOBAL_HANDLES_H_