Move test.dart's check for missing test directories from co19 to general framework.

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.
 
 #library("test_suite");
 
 #import("dart:io");
 #import("status_file_parser.dart");
 #import("test_runner.dart");
 #import("multitest.dart");
@@ skipping 209 matching lines @@
                                statusFileRead);
     }
   }
 
   void processDirectory() {
     directoryPath = '$dartDir/$directoryPath';
     Directory dir = new Directory(directoryPath);
     dir.errorHandler = (s) {
       throw s;
     };
-    dir.fileHandler = processFile;
-    dir.doneHandler = directoryListingDone;
-    dir.list(recursive: listRecursively());
+    dir.existsHandler = (bool exists) {
+      if (!exists) {
+        print('Directory containing tests not found: $directoryPath');
+        directoryListingDone(false);
+      } else {      
+        dir.fileHandler = processFile;
+        dir.doneHandler = directoryListingDone;
+        dir.list(recursive: listRecursively());
+      }
+    };
+    dir.exists();
   }
 
   void enqueueTestCaseFromTestInformation(TestInformation info) {
     var filename = info.filename;
     var optionsFromFile = info.optionsFromFile;
     var isNegative = info.isNegative;
 
     // Look up expectations in status files using a modified file path.
     String testName;
     filename = filename.replaceAll('\\', '/');
@@ skipping 823 matching lines @@
  * $noCrash tests are expected to be flaky but not crash
  * $pass tests are expected to pass
  * $failOk tests are expected to fail that we won't fix
  * $fail tests are expected to fail that we should fix
  * $crash tests are expected to crash that we should fix
  * $timeout tests are allowed to timeout
 """;
     print(report);
    }
 }