Change directory owner listing to list joint owners together.

third_party/WebKit/Tools/Scripts/webkitpy/w3c/directory_owners_extractor_unittest.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/w3c/directory_owners_extractor_unittest.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/w3c/directory_owners_extractor_unittest.py b/third_party/WebKit/Tools/Scripts/webkitpy/w3c/directory_owners_extractor_unittest.py
index 3fbfc496cb929d59cb521e41e8b42cbde2affd4b..213e436bbcb2489c2933b022a1ac10b3567e8acf 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/w3c/directory_owners_extractor_unittest.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/w3c/directory_owners_extractor_unittest.py
@@ -37,9 +37,9 @@ class DirectoryOwnersExtractorTest(unittest.TestCase):
 
     def test_list_owners(self):
         self.extractor.owner_map = {
-            'external/wpt/foo': ['a@chromium.org'],
+            'external/wpt/foo': ['a@chromium.org', 'c@chromium.org'],
             'external/wpt/bar': ['b@chromium.org'],
-            'external/wpt/baz': ['a@chromium.org'],
+            'external/wpt/baz': ['a@chromium.org', 'c@chromium.org'],
         }
         self.filesystem.files = {
             '/mock-checkout/third_party/WebKit/LayoutTests/external/wpt/foo/x/y.html': '',
@@ -54,7 +54,7 @@ class DirectoryOwnersExtractorTest(unittest.TestCase):
         ]
         self.assertEqual(
             self.extractor.list_owners(changed_files),
-            {'a@chromium.org': ['external/wpt/foo', 'external/wpt/baz']})
+            {('a@chromium.org', 'c@chromium.org'): ['external/wpt/foo', 'external/wpt/baz']})
 
     def test_extract_owner_positive_cases(self):
         self.assertEqual(self.extractor.extract_owners('## Owners: foo@chromium.org'), ['foo@chromium.org'])