Add URL recipe module from "depot_tools".

recipe_modules/url/tests/validate_url.py

+# Copyright 2017 The LUCI Authors. All rights reserved.
+# Use of this source code is governed under the Apache License, Version 2.0
+# that can be found in the LICENSE file.
+
+DEPS = [
+  'properties',
+  'step',
+  'url',
+]
+
+
+def RunSteps(api):
+  api.url.validate_url(api.properties['url_to_validate'])
+
+
+def GenTests(api):
+  yield (api.test('basic') +
+      api.properties(url_to_validate='https://example.com'))
+
+  yield (api.test('no_scheme') +
+      api.properties(url_to_validate='example.com') +
+      api.expect_exception('ValueError'))
+
+  yield (api.test('invalid_scheme') +
+      api.properties(url_to_validate='ftp://example.com') +
+      api.expect_exception('ValueError'))
+
+  yield (api.test('no_host') +
+      api.properties(url_to_validate='https://') +
+      api.expect_exception('ValueError'))