Add true_type_tag utility function

src/servo/servo.rc

@@ -84,6 +84,7 @@ mod text {
         #[cfg(target_os = "linux")]
         mod ft_native_font;
     }
+    mod util;
 }
 
 mod util {

src/servo/text/util.rs

@@ -0,0 +1,11 @@
+export true_type_tag;
+
+#[doc = "Generate a 32-bit TrueType tag from its 4 charecters"]
+fn true_type_tag(a: char, b: char, c: char, d: char) -> u32 {
+    (a << 24 | b << 16 | c << 8 | d) as u32
+}
+
+#[test]
+fn test_true_type_tag() {
+    assert true_type_tag('c', 'm', 'a', 'p') == 0x_63_6D_61_70_u32;
+}