Don't test for file differences in the polling watcher.

pkg/watcher/test/directory_watcher/linux_test.dart

Index: pkg/watcher/test/directory_watcher/linux_test.dart
diff --git a/pkg/watcher/test/directory_watcher/linux_test.dart b/pkg/watcher/test/directory_watcher/linux_test.dart
index f53b272b4578a50b842505cfaa680637093e4cec..c2d017677d639862d727e7fc297a959ef2afaf97 100644
--- a/pkg/watcher/test/directory_watcher/linux_test.dart
+++ b/pkg/watcher/test/directory_watcher/linux_test.dart
@@ -23,16 +23,6 @@ main() {
         new isInstanceOf<LinuxDirectoryWatcher>());
   });
 
-  test('notifies even if the file contents are unchanged', () {
-    writeFile("a.txt", contents: "same");
-    writeFile("b.txt", contents: "before");
-    startWatcher();
-    writeFile("a.txt", contents: "same");
-    writeFile("b.txt", contents: "after");
-    expectModifyEvent("a.txt");
-    expectModifyEvent("b.txt");
-  });
-
   test('emits events for many nested files moved out then immediately back in',
       () {
     withPermutations((i, j, k) =>