Make isEmpty a getter.

lib/compiler/implementation/tree_validator.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.
 
 class TreeValidatorTask extends CompilerTask {
   TreeValidatorTask(Compiler compiler) : super(compiler);
 
   void validate(Node tree) {
     assert(check(tree));
   }
 
   bool check(Node tree) {
     List<InvalidNodeError> errors = [];
     void report(node, message) {
       final error = new InvalidNodeError(node, message);
       errors.add(error);
       compiler.reportWarning(node, message);
     };
     final validator = new ValidatorVisitor(report);
     tree.accept(new TraversingVisitor(validator));
 
-    return errors.isEmpty();
+    return errors.isEmpty;
   }
 }
 
 class ValidatorVisitor extends Visitor {
   final Function reportInvalidNode;
 
   ValidatorVisitor(Function this.reportInvalidNode);
 
   expect(Node node, bool test, [message]) {
     if (!test) reportInvalidNode(node, message);
   }
 
   visitNode(Node node) {}
 
   visitSendSet(SendSet node) {
     final selector = node.selector;
     final name = node.assignmentOperator.source.stringValue;
     final arguments = node.arguments;
 
     expect(node, arguments != null);
     expect(node, selector is Identifier, 'selector is not assignable');
     if (identical(name, '++') || identical(name, '--')) {
       expect(node, node.assignmentOperator is Operator);
       if (node.isIndex) {
-        expect(node.arguments.tail.head, node.arguments.tail.isEmpty());
+        expect(node.arguments.tail.head, node.arguments.tail.isEmpty);
       } else {
-        expect(node.arguments.head, node.arguments.isEmpty());
+        expect(node.arguments.head, node.arguments.isEmpty);
       }
     } else {
-      expect(node, !node.arguments.isEmpty());
+      expect(node, !node.arguments.isEmpty);
     }
   }
 
   visitReturn(Return node) {
     if (!node.isRedirectingFactoryBody && node.hasExpression) {
       // We allow non-expression expressions in Return nodes, but only when
       // using them to hold redirecting factory constructors.
       expect(node, node.expression.asExpression() != null);
     }
   }
 }
 
 class InvalidNodeError {
   final Node node;
   final String message;
   InvalidNodeError(this.node, [this.message]);
 
   toString() {
     String nodeString = node.toDebugString();
     String result = 'invalid node: $nodeString';
     if (message != null) result = '$result ($message)';
     return result;
   }
 }