Use VM type cast and save handles.

runtime/vm/ast.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_AST_H_
 #define VM_AST_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/growable_array.h"
@@ skipping 294 matching lines @@
 };
 
 
 class LiteralNode : public AstNode {
  public:
   LiteralNode(intptr_t token_pos, const Instance& literal)
       : AstNode(token_pos), literal_(literal) {
     ASSERT(literal.IsZoneHandle());
 #if defined(DEBUG)
     if (literal.IsString()) {
-      String& str = String::Handle();
-      str ^= literal.raw();
-      ASSERT(str.IsSymbol());
+      ASSERT(String::Cast(literal).IsSymbol());
     }
 #endif  // defined(DEBUG)
     ASSERT(literal.IsNull() ||
            Class::Handle(literal.clazz()).is_finalized() ||
            Class::Handle(literal.clazz()).is_prefinalized());
   }
 
   const Instance& literal() const { return literal_; }
 
   virtual const Instance* EvalConstExpr() const {
@@ skipping 1348 matching lines @@
   const LocalVariable& context_var_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(InlinedFinallyNode);
 };
 
 }  // namespace dart
 
 #undef DECLARE_COMMON_NODE_FUNCTIONS
 
 #endif  // VM_AST_H_