Replace ToAsciiVector and ToUC16Vector with single function that returns a tagged value.

test/mjsunit/string-split.js

Index: test/mjsunit/string-split.js
diff --git a/test/mjsunit/string-split.js b/test/mjsunit/string-split.js
index 6fcf55799e5b3f3b876c972414fd8052caf0fa67..9a5bb43f4a3b665d1c477d367dfa6b85808b3da5 100644
--- a/test/mjsunit/string-split.js
+++ b/test/mjsunit/string-split.js
@@ -116,3 +116,14 @@ assertEquals(["a", "b", "c"], "abc".split("", 3));
 assertEquals(["a", "b", "c"], "abc".split("", numberObj(3)));
 assertEquals(["a", "b", "c"], "abc".split("", 4));
 assertEquals(["a", "b", "c"], "abc".split("", numberObj(4)));
+
+var all_ascii_chars = [];
+for (var i = 0; i < 128; i++) all_ascii_chars[i] = String.fromCharCode(i);
+var all_ascii_string = all_ascii_chars.join("");
+
+var split_chars = all_ascii_string.split("");
+assertEquals(128, split_chars.length);
+for (var i = 0; i < 128; i++) {
+  assertEquals(1, split_chars[i].length);
+  assertEquals(i, split_chars[i].charCodeAt(0));
+}