[tst][add] Marionette test: URI without host

Convert Mozmill test "testRequestLog/testUriWithoutHost.js" to
Marionette.

The test is in fact not about the Request Log, more about such
URIs in general, so the Marionette test uses the "Requests" API
instead of the "RequestLog" UI library, which is faster.

tests/marionette/tests/policy/manifest.ini

@@ -1 +1,2 @@
 [test_rule_with_scheme_only.py]
+[test_uris.py]

tests/marionette/tests/policy/test_uris.py

@@ -0,0 +1,47 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+from rp_ui_harness.testcases import RequestPolicyTestCase
+
+
+class TestUris(RequestPolicyTestCase):
+    """Class for testing specific URI types."""
+
+    def setUp(self):
+        super(TestUris, self).setUp()
+
+        self.marionette.set_context("content")
+
+    def tearDown(self):
+        try:
+            self.requests.stop_listening()
+            self.marionette.set_context("chrome")
+        finally:
+            super(TestUris, self).tearDown()
+
+    def test_uri_without_host(self):
+        url = "http://www.maindomain.test/scheme-unknown-and-without-host.html"
+
+        self.requests.start_listening()
+
+        def get_requests_by_dest(dest_uri):
+            return [request
+                    for request in self.requests.all
+                    if request["dest"] == dest_uri]
+
+        with self.marionette.using_context("content"):
+            self.marionette.navigate(url)
+
+            link = self.marionette.find_element("tag name", "a")
+            link_uri = link.get_attribute("href")
+
+        self.assertEqual(len(get_requests_by_dest(link_uri)), 0,
+                         ("There hasn't been any request to '{}' yet."
+                          .format(link_uri)))
+
+        link.click()
+
+        self.assertEqual(len(get_requests_by_dest(link_uri)), 1,
+                         ("There has been exactly one request to '{}'."
+                          .format(link_uri)))