Add SkipSlow marker

tools/testing/dart/test_suite.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 enumerating and preparing tests.
  *
  * This library includes:
  *
  * - Creating tests by listing all the Dart files in certain directories,
@@ skipping 274 matching lines @@
           new CompilerConfiguration(configuration).hasCompiler) {
         summaryReport.addCompileErrorSkipTest();
         return;
       } else {
         summaryReport.add(testCase);
       }
     }
 
     // Handle skipped tests
     if (expectations.contains(Expectation.SKIP) ||
-        expectations.contains(Expectation.SKIP_BY_DESIGN)) {
+        expectations.contains(Expectation.SKIP_BY_DESIGN) ||
+        expectations.contains(Expectation.SKIP_SLOW)) {
       return;
     }
 
     doTest(testCase);
   }
 
   String createGeneratedTestDirectoryHelper(
       String name, String dirname, Path testPath, String optionsName) {
     Path relative = testPath.relativeTo(TestUtils.dartDir);
     relative = relative.directoryPath.append(relative.filenameWithoutExtension);
@@ skipping 2082 matching lines @@
       for (var key in PATH_REPLACEMENTS.keys) {
         if (path.startsWith(key)) {
           path = path.replaceFirst(key, PATH_REPLACEMENTS[key]);
           break;
         }
       }
     }
     return path;
   }
 }