Remove deprecated <, <=, >, and >= of DateTime.

tools/testing/dart/test_runner.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
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * Classes and methods for executing tests.
  *
  * This module includes:
  * - Managing parallel execution of tests, including timeout checks.
  * - Evaluating the output of each test as pass/fail/crash/timeout.
@@ skipping 143 matching lines @@
     return readDepsFile("$_outputFile.deps").then((dependencies) {
       if (dependencies != null) {
         dependencies.addAll(_bootstrapDependencies);
         var jsOutputLastModified = TestUtils.lastModifiedCache.getLastModified(
             new Uri.fromComponents(scheme: 'file', path: _outputFile));
         if (jsOutputLastModified != null) {
           for (var dependency in dependencies) {
             var dependencyLastModified =
                 TestUtils.lastModifiedCache.getLastModified(dependency);
             if (dependencyLastModified == null ||
-                dependencyLastModified > jsOutputLastModified) {
+                dependencyLastModified.isAfter(jsOutputLastModified)) {
               return false;
             }
           }
           return true;
         }
       }
       return false;
     });
   }
 }
@@ skipping 1548 matching lines @@
     }
   }
 
   void eventAllTestsDone() {
     for (var listener in _eventListener) {
       listener.allDone();
     }
   }
 }