dart2js cps: Add CharCodeAt builtin.

tests/compiler/dart2js/js_backend_cps_ir_codeUnitAt_test.dart

+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Tests for constant folding and lowering String.codeUnitAt.
+
+library basic_tests;
+
+import 'js_backend_cps_ir.dart';
+
+const List<TestEntry> tests = const [
+
+  // Constant folding.
+  const TestEntry(r"""
+main() {
+  print('A'.codeUnitAt(0));
+}""",r"""
+function() {
+  P.print(65);
+}"""),
+
+
+  // Bounds checking.
+  const TestEntry.forMethod('function(foo)',
+r"""
+foo(s) {
+  var sum = 0;
+  for (int i = 0; i < s.length; i++) sum += s.codeUnitAt(i);
+  return sum;
+}
+main() {
+  print(foo('ABC'));
+  print(foo('Hello'));
+}""",r"""
+function(s) {
+  var v0 = s.length, sum = 0, i = 0;
+  for (; i < v0; sum = sum + s.charCodeAt(i), i = i + 1)
+    ;
+  return sum;
+}"""),
+];
+
+
+void main() {
+  runTests(tests);
+}