Fix build: use strings for booleans in status expression evaluation.

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 92 matching lines @@
 
   String termValue(environment) => value;
 }
      
 
 class BooleanVariable implements BooleanExpression {
   TermVariable variable;
 
   BooleanVariable(this.variable);
 
-  bool evaluate(environment) => variable.termValue(environment) == true;
+  bool evaluate(environment) => variable.termValue(environment) == 'true';
   String toString() => "(bool \$${variable.name})";
 }
 
 
 class BooleanOperation implements BooleanExpression {
   String op;
   BooleanExpression left;
   BooleanExpression right;
 
   BooleanOperation(this.op, this.left, this.right);
@@ skipping 165 matching lines @@
           "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);
     } 
   }
 }