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

include/v8-profiler.h

 // Copyright 2010 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 412 matching lines @@
   static void DefineWrapperClass(
       uint16_t class_id,
       WrapperInfoCallback callback);
 
   /**
    * Default value of persistent handle class ID. Must not be used to
    * define a class. Can be used to reset a class of a persistent
    * handle.
    */
   static const uint16_t kPersistentHandleNoClassId = 0;
+
+  /** Returns the number of currently existing persistent handles. */
+  static int GetPersistentHandleCount();
 };
 
 
 /**
  * Interface for providing information about embedder's objects
  * held by global handles. This information is reported in two ways:
  *
  *  1. When calling AddObjectGroup, an embedder may pass
  *     RetainedObjectInfo instance describing the group.  To collect
  *     this information while taking a heap snapshot, V8 calls GC
@@ skipping 64 matching lines @@
 };
 
 
 }  // namespace v8
 
 
 #undef V8EXPORT
 
 
 #endif  // V8_V8_PROFILER_H_