Add URL recipe module from "depot_tools".

recipe_modules/url/tests/join.py

Index: recipe_modules/url/tests/join.py
diff --git a/recipe_modules/url/tests/join.py b/recipe_modules/url/tests/join.py
new file mode 100644
index 0000000000000000000000000000000000000000..049f6ce8468afcaf866de13bfddbfdb6ba974faf
--- /dev/null
+++ b/recipe_modules/url/tests/join.py
@@ -0,0 +1,23 @@
+# 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 = [
+  'step',
+  'url',
+]
+
+
+def RunSteps(api):
+  api.step('step1',
+           ['/bin/echo', api.url.join('foo', 'bar', 'baz')])
+  api.step('step2',
+           ['/bin/echo', api.url.join('foo/', '/bar/', '/baz')])
+  api.step('step3',
+           ['/bin/echo', api.url.join('//foo/', '//bar//', '//baz//')])
+  api.step('step4',
+           ['/bin/echo', api.url.join('//foo/bar//', '//baz//')])
+
+
+def GenTests(api):
+  yield api.test('basic')