Regenerate MANIFEST.json when WPT tests are run

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/controllers/manager_unittest.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/controllers/manager_unittest.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/controllers/manager_unittest.py b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/controllers/manager_unittest.py
index 7803e5b233037e7f6f652ae0d10d1e82ec362da9..13f04ae84220ded60f6af23798f0252ea71335be 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/controllers/manager_unittest.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/controllers/manager_unittest.py
@@ -178,3 +178,13 @@ class ManagerTest(unittest.TestCase):
             if not port.host.filesystem.exists(dir_name):
                 deleted_dir_count = deleted_dir_count + 1
         self.assertEqual(deleted_dir_count, 5)
+
+    def test_copies_manifest_if_not_there_already(self):
+        host = MockHost()
+        port = host.port_factory.get('test-mac-mac10.10')
+        port.host.filesystem.write_binary_file('/test.checkout/LayoutTests/external/WPT_BASE_MANIFEST.json', '{}')
+
+        self.assertFalse(port.host.filesystem.exists('/test.checkout/LayoutTests/external/wpt/MANIFEST.json'))
+        manager = Manager(port, options=optparse.Values({'max_locked_shards': 1}), printer=FakePrinter())
+        manager.run([])
+        self.assertTrue(port.host.filesystem.exists('/test.checkout/LayoutTests/external/wpt/MANIFEST.json'))