Add str.rs.

src/components/util/str.rs

@@ -0,0 +1,21 @@
+/* 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/. */
+
+pub type DOMString = ~str;
+
+pub fn null_str_as_empty(s: &Option<DOMString>) -> DOMString {
+    // We don't use map_default because it would allocate ~"" even for Some.
+    match *s {
+        Some(ref s) => s.clone(),
+        None => ~""
+    }
+}
+
+pub fn null_str_as_empty_ref<'a>(s: &'a Option<DOMString>) -> &'a str {
+    match *s {
+        Some(ref s) => s.as_slice(),
+        None => &'a ""
+    }
+}
+