Move Zone's destructor out of a header file.

runtime/vm/symbols.cc

 // 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.
 
 #include "vm/symbols.h"
 
 #include "vm/handles.h"
-#include "vm/handles_impl.h"
 #include "vm/hash_table.h"
 #include "vm/isolate.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/raw_object.h"
 #include "vm/reusable_handles.h"
 #include "vm/snapshot_ids.h"
 #include "vm/unicode.h"
 #include "vm/visitor.h"
 
@@ skipping 719 matching lines @@
 RawObject* Symbols::GetPredefinedSymbol(intptr_t object_id) {
   ASSERT(IsPredefinedSymbolId(object_id));
   intptr_t i = (object_id - kMaxPredefinedObjectIds);
   if ((i > kIllegal) && (i < Symbols::kMaxPredefinedId)) {
     return symbol_handles_[i]->raw();
   }
   return Object::null();
 }
 
 }  // namespace dart