Roll to pickup pool changes

packages/csslib/example/call_parser.dart

 // 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
 
 import 'package:csslib/parser.dart' as css;
 import 'package:csslib/visitor.dart';
 
 const _default = const css.PreprocessorOptions(
     useColors: false,
     checked: true,
     warningsAsErrors: true,
@@ skipping 25 matching lines @@
       '@import "support/at-charset-019.css"; div { color: red; }'
       'button[type] { background-color: red; }'
       '.foo { '
       'color: red; left: 20px; top: 20px; width: 100px; height:200px'
       '}'
       '#div {'
       'color : #00F578; border-color: #878787;'
       '}',
       errors: errors);
 
-  if (!errors.isEmpty) {
+  if (errors.isNotEmpty) {
     print("Got ${errors.length} errors.\n");
     for (var error in errors) {
       print(error);
     }
   } else {
     print(prettyPrint(stylesheet));
   }
 
   // Parse a stylesheet with errors
   print('2. Catch severe syntax errors:');
   print('   ===========================');
   var stylesheetError = parseCss(
       '.foo #%^&*asdf{ '
       'color: red; left: 20px; top: 20px; width: 100px; height:200px'
       '}',
       errors: errors);
 
-  if (!errors.isEmpty) {
+  if (errors.isNotEmpty) {
     print("Got ${errors.length} errors.\n");
     for (var error in errors) {
       print(error);
     }
   } else {
     print(stylesheetError.toString());
   }
 
   // Parse a stylesheet that warns (checks) problematic CSS.
   print('3. Detect CSS problem with checking on:');
   print('   ===================================');
   stylesheetError = parseCss('# div1 { color: red; }', errors: errors);
 
-  if (!errors.isEmpty) {
+  if (errors.isNotEmpty) {
     print("Detected ${errors.length} problem in checked mode.\n");
     for (var error in errors) {
       print(error);
     }
   } else {
     print(stylesheetError.toString());
   }
 
   // Parse a CSS selector.
   print('4. Parse a selector only:');
   print('   ======================');
   var selectorAst = css.selector('#div .foo', errors: errors);
-  if (!errors.isEmpty) {
+  if (errors.isNotEmpty) {
     print("Got ${errors.length} errors.\n");
     for (var error in errors) {
       print(error);
     }
   } else {
     print(prettyPrint(selectorAst));
   }
 }