Fix type error in tools/testing/dart/status_expression.dart.

tools/testing/dart/status_expression.dart

 // Copyright (c) 2011, 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.
 
 #library("status_expression");
 
 /**
  * Parse and evaluate expressions in a .status file for Dart and V8.
  * There are set expressions and Boolean expressions in a .status file.
  * The grammar is:
@@ skipping 249 matching lines @@
       scanner.advance();
       BooleanExpression right = parseBooleanAtomic();
       left = new BooleanOperation(Token.AND, left, right);
     }
     return left;
   }
 
   BooleanExpression parseBooleanAtomic() {
     if (scanner.current == Token.LEFT_PAREN) {
       scanner.advance();
-      SetExpression value = parseBooleanExpression();
+      BooleanExpression value = parseBooleanExpression();
       Expect.equals(scanner.current, Token.RIGHT_PAREN,
                     "Missing right parenthesis in expression");
       scanner.advance();
       return value;
     }
 
     // The only atomic booleans are of the form $variable == value or the
     // form $variable.
     Expect.equals(scanner.current, Token.DOLLAR_SYMBOL,
         "Expected \$ in expression, got ${scanner.current}");
     scanner.advance();
     Expect.isTrue(const RegExp(@"^\w+$").hasMatch(scanner.current),
         "Expected identifier in expression, got ${scanner.current}");
     TermVariable left = new TermVariable(scanner.current);
     scanner.advance();
     if (scanner.current == Token.EQUALS) {
       scanner.advance();
       Expect.isTrue(const RegExp(@"^\w+$").hasMatch(scanner.current),
           "Expected identifier in expression, got ${scanner.current}");
       TermConstant right = new TermConstant(scanner.current);
       scanner.advance();
       return new Comparison(left, right);
     } else {
       return new BooleanVariable(left);
     } 
   }
 }