Signal an error for File.lastModified on a directory

tests/standalone/io/file_test.dart

 // Copyright (c) 2013, 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.
 //
 // Dart test program for testing file I/O.
 
 // OtherResources=empty_file
 // OtherResources=file_test.txt
 // OtherResources=fixed_length_file
 // OtherResources=read_as_text.dat
@@ skipping 1250 matching lines @@
     getLength();
     Expect.throws(() => file.lengthSync());
   }
 
   static void testLastModifiedSync() {
     var modified = new File(Platform.executable).lastModifiedSync();
     Expect.isTrue(modified is DateTime);
     Expect.isTrue(modified.isBefore(new DateTime.now()));
   }
 
+  static void testLastModifiedSyncDirectory() {
+    Directory tmp = tempDirectory.createTempSync('file_last_modified_test_');
+    String dirPath = '${tmp.path}/dir';
+    new Directory(dirPath).createSync();
+    try {
+      new File(dirPath).lastModifiedSync();
+      Expect.fail('Expected operation to throw');
+    } catch (e) {
+      if (e is! FileSystemException) {
+        print(e);
+      }
+      Expect.isTrue(e is FileSystemException);
+    } finally {
+      tmp.deleteSync(recursive: true);
+    }
+  }
+
   // Test that opens the same file for writing then for appending to test
   // that the file is not truncated when opened for appending.
   static void testAppend() {
     asyncTestStarted();
     var file = new File('${tempDirectory.path}/out_append');
     file.open(mode: WRITE).then((openedFile) {
       openedFile.writeString("asdf").then((ignore) {
         openedFile.close().then((ignore) {
           file.open(mode: APPEND).then((openedFile) {
             openedFile.length().then((length) {
@@ skipping 196 matching lines @@
       testWriteVariousLists();
       testDirectory();
       testDirectorySync();
       testWriteStringUtf8();
       testWriteStringUtf8Sync();
       testRename(targetExists: false);
       testRenameSync(targetExists: false);
       testRename(targetExists: true);
       testRenameSync(targetExists: true);
       testLastModified();
+      testLastModifiedSyncDirectory();
       testDoubleAsyncOperation();
       asyncEnd();
     });
   }
 }
 
 main() {
   FileTest.testMain();
 }