Resolution for issue #5092: Unit test handle checks consider dangling handles to be valid.

runtime/vm/thread_registry.h

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef RUNTIME_VM_THREAD_REGISTRY_H_
 #define RUNTIME_VM_THREAD_REGISTRY_H_
 
 #include "vm/globals.h"
 #include "vm/growable_array.h"
 #include "vm/isolate.h"
@@ skipping 22 matching lines @@
   void PrepareForGC();
   Thread* mutator_thread() const { return mutator_thread_; }
 
 #ifndef PRODUCT
   void PrintJSON(JSONStream* stream) const;
 #endif
 
   // Calculates the sum of the max memory usage in bytes of each thread.
   uintptr_t ThreadHighWatermarksTotalLocked() const;
 
+  bool IsValidHandle(Dart_Handle handle) const;
   intptr_t CountZoneHandles() const;
   intptr_t CountScopedHandles() const;
 
  private:
   Thread* active_list() const { return active_list_; }
   Monitor* threads_lock() const { return threads_lock_; }
 
   Thread* GetFreeThreadLocked(Isolate* isolate, bool is_mutator);
   void ReturnThreadLocked(bool is_mutator, Thread* thread);
   void AddToActiveListLocked(Thread* thread);
@@ skipping 23 matching lines @@
   Thread* mutator_thread_;
 
   friend class Isolate;
   friend class SafepointHandler;
   DISALLOW_COPY_AND_ASSIGN(ThreadRegistry);
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_THREAD_REGISTRY_H_