Use the integer type to get rid of above 0 checks in bounds checks.

tests/compiler/dart2js/value_range3_test.dart

+// Copyright (c) 2013, 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.
+
+// Test that global analysis in dart2js propagates positive integers.
+
+import 'package:expect/expect.dart';
+import "package:async_helper/async_helper.dart";
+import 'memory_compiler.dart';
+
+const MEMORY_SOURCE_FILES = const {
+  'main.dart': '''
+
+var a = [42];
+
+main() {
+  var value = a[0];
+  if (value < 42) {
+    return new List(42)[value];
+  }
+}
+''',
+};
+
+main() {
+  var compiler = compilerFor(MEMORY_SOURCE_FILES);  
+  asyncTest(() => compiler.run(Uri.parse('memory:main.dart')).then((_) {
+    var element = compiler.mainApp.findExported('main');
+    var code = compiler.backend.assembleCode(element);
+    Expect.isFalse(code.contains('ioore'));
+  }));
+}
+