Implement WebIDL codegen for ByteString.

src/components/script/dom/bindings/str.rs

@@ -0,0 +1,16 @@
+/* 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 struct ByteString(Vec<u8>);
+
+impl ByteString {
+    pub fn new(value: Vec<u8>) -> ByteString {
+        ByteString(value)
+    }
+
+    pub fn as_slice<'a>(&'a self) -> &'a [u8] {
+        let ByteString(ref vector) = *self;
+        vector.as_slice()
+    }
+}