Correctly visit all external strings.

include/v8.h

 // Copyright 2012 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 3426 matching lines @@
    */
   static bool Dispose();
 
   /**
    * Get statistics about the heap memory usage.
    */
   static void GetHeapStatistics(HeapStatistics* heap_statistics);
 
   /**
    * Iterates through all external resources referenced from current isolate
-   * heap. This method is not expected to be used except for debugging purposes
-   * and may be quite slow.
+   * heap.  GC is not invoked prior to iterating, therefore there is no
+   * guarantee that visited objects are still alive.
    */
   static void VisitExternalResources(ExternalResourceVisitor* visitor);
 
   /**
    * Iterates through all the persistent handles in the current isolate's heap
    * that have class_ids.
    */
   static void VisitHandlesWithClassIds(PersistentHandleVisitor* visitor);
 
   /**
@@ skipping 1237 matching lines @@
 
 
 }  // namespace v8
 
 
 #undef V8EXPORT
 #undef TYPE_CHECK
 
 
 #endif  // V8_H_