Chrome Version: 56.0.2924.87

Chrome fails the web-platform-tests test "Invalid referrerPolicy attribute value" for the link element specifically. It seems that referrerPolicy="not-a-valid-value" will be reflected in the `elem.referrerPolicy` getter even though it shouldn't be (and isn't for other elements).

The failing WPT is referrer-policy/generic/subresource-test/attr-referrer-invalid-value.html:

      test(function () {
          var elements = ["iframe", "img", "a", "area", "link"];
          for (var i = 0; i < elements.length; i++) {
              var elem = document.createElement(elements[i]);
              elem.referrerPolicy = "unsafe-url";
              assert_equals(elem.referrerPolicy, "unsafe-url");
              elem.referrerPolicy = "not-valid-value";
              assert_equals(elem.referrerPolicy, "");
          }
      }, "Invalid referrerpolicy values not reflected");