VM: Fix memory leak during shutdown

runtime/platform/hashmap.h

 // Copyright (c) 2012, 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_PLATFORM_HASHMAP_H_
 #define RUNTIME_PLATFORM_HASHMAP_H_
 
 #include "platform/globals.h"
 
 namespace dart {
@@ skipping 43 matching lines @@
   };
 
   // If an entry with matching key is found, Lookup()
   // returns that entry. If no matching entry is found,
   // but insert is set, a new entry is inserted with
   // corresponding key, key hash, and NULL value.
   // Otherwise, NULL is returned.
   Entry* Lookup(void* key, uint32_t hash, bool insert);
 
   // Removes the entry with matching key.
+  //
+  // WARNING: This method cannot be called while iterating a `HashMap`
+  // otherwise the iteration might step over elements!
   void Remove(void* key, uint32_t hash);
 
+  // Removes the entry and returns the next entry (in iteration order) after
+  // this one.
+  //
+  // Usage instructions for removing elements during iteration:
+  //
+  //    HashMap::Entry* current = map.Start();
+  //    while (current != NULL) {
+  //       ...
+  //      if (condition) {
+  //        current = map.Remove(current);
+  //      } else {
+  //        current = map.Next(current);
+  //      }
+  //    }
+  //
+  Entry* Remove(Entry* entry);
+
   // Empties the hash map (occupancy() == 0), and calls the function 'clear' on
   // each of the values if given.
   void Clear(ClearFun clear = NULL);
 
   // The number of entries stored in the table.
   intptr_t size() const { return occupancy_; }
 
   // The capacity of the table. The implementation
   // makes sure that occupancy is at most 80% of
   // the table capacity.
@@ skipping 21 matching lines @@
   void Initialize(uint32_t capacity);
   void Resize();
 
   friend class IntSet;  // From hashmap_test.cc
   DISALLOW_COPY_AND_ASSIGN(HashMap);
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_PLATFORM_HASHMAP_H_