Convert all symbols accessor to return read only handles so that it is not necessary to create a ne…

vm/scopes.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_SCOPES_H_
 #define VM_SCOPES_H_
 
 #include "vm/allocation.h"
 #include "vm/assembler.h"
 #include "vm/growable_array.h"
@@ skipping 130 matching lines @@
       join_for_break_(NULL),
       join_for_continue_(NULL),
       is_continue_target_(false) {
   }
 
   static SourceLabel* New(intptr_t token_pos, String* name, Kind kind) {
     if (name != NULL) {
       return new SourceLabel(token_pos, *name, kind);
     } else {
       return new SourceLabel(token_pos,
-                             String::ZoneHandle(Symbols::DefaultLabel()),
+                             Symbols::DefaultLabel(),
                              kind);
     }
   }
 
   intptr_t token_pos() const { return token_pos_; }
   const String& name() const { return name_; }
   LocalScope* owner() const { return owner_; }
   void set_owner(LocalScope* owner) {
     ASSERT(owner_ == NULL);
     owner_ = owner;
@@ skipping 199 matching lines @@
   intptr_t end_token_pos_;    // Token index of end of scope.
   GrowableArray<LocalVariable*> variables_;
   GrowableArray<SourceLabel*> labels_;
 
   DISALLOW_COPY_AND_ASSIGN(LocalScope);
 };
 
 }  // namespace dart
 
 #endif  // VM_SCOPES_H_