Also archive diff files in layout-test-results.zip.

scripts/slave/chromium/archive_layout_test_results_unittest.py

 #!/usr/bin/env python
 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import os
 import sys
 import unittest
 
 BASE_DIR = os.path.join(
@@ skipping 20 matching lines @@
     self.assertTrue(archive_layout_test_results._IsActualResultFile(
         'foo-actual.txt'))
     self.assertTrue(archive_layout_test_results._IsActualResultFile(
         'foo-actual.png'))
 
     self.assertFalse(archive_layout_test_results._IsActualResultFile(
         'foo-actual.jpg'))
     self.assertFalse(archive_layout_test_results._IsActualResultFile(
         'foo-actual.html'))
 
+  def test_IsDiffFile(self):
+    self.assertTrue(archive_layout_test_results._IsDiffFile('a-diff.png'))
+    self.assertTrue(archive_layout_test_results._IsDiffFile('a-diff.txt'))
+    self.assertTrue(archive_layout_test_results._IsDiffFile('a-wdiff.txt'))
+    self.assertTrue(archive_layout_test_results._IsDiffFile('a-expected.txt'))
+    self.assertTrue(archive_layout_test_results._IsDiffFile('a-expected.html'))
+
+    self.assertFalse(archive_layout_test_results._IsDiffFile('a-diff.png.foo'))
+    self.assertFalse(archive_layout_test_results._IsDiffFile('a-diff.png.foo'))
+    self.assertFalse(archive_layout_test_results._IsDiffFile('foo-actual.html'))
+    self.assertFalse(archive_layout_test_results._IsDiffFile('results.html'))
+
 
 if __name__ == '__main__':
   unittest.main()