Fix length computation on init.mangledNames.

tests/lib/mirrors/reflect_two_classes_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.
+
+// This is a regression test for http://dartbug.com/23054
+
+library index;
+
+@MirrorsUsed(targets: const [Bar, Foo], symbols: const ['bar', 'getBar', 'foo', 'getFoo'], override: '*')
+import 'dart:mirrors';
+
+import 'package:expect/expect.dart';
+
+main() {
+  var bar = new Bar();
+  var barMirror = reflect(bar);
+  Expect.equals(42, barMirror.getField(#bar).reflectee, "bar field");
+  Expect.equals(42, barMirror.invoke(#getBar, []).reflectee, "getBar Method");
+
+  var foo = new Foo();
+  var fooMirror = reflect(foo);
+  Expect.equals(9, fooMirror.getField(#foo).reflectee, "foo field");
+  Expect.equals(9, fooMirror.invoke(#getFoo, []).reflectee, "getFoo Method");
+}
+
+class Bar {
+  int bar = 42;
+
+  int getBar() => bar;
+}
+
+class Foo {
+  int foo = 9;
+
+  int getFoo() => foo;
+}
+