Use clustered serialization for full snapshots.

runtime/vm/symbols.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 VM_SYMBOLS_H_
 #define VM_SYMBOLS_H_
 
 #include "vm/growable_array.h"
 #include "vm/object.h"
 #include "vm/snapshot_ids.h"
@@ skipping 657 matching lines @@
   // used in generated dart code for direct access to these objects.
   static RawString* predefined_[kNumberOfOneCharCodeSymbols];
 
   // List of handles for predefined symbols.
   static String* symbol_handles_[kMaxPredefinedId];
 
   friend class Dart;
   friend class String;
   friend class SnapshotReader;
   friend class SnapshotWriter;
+  friend class Serializer;
+  friend class Deserializer;
   friend class ApiMessageReader;
 
   DISALLOW_COPY_AND_ASSIGN(Symbols);
 };
 
 }  // namespace dart
 
 #endif  // VM_SYMBOLS_H_