Fix bug https://code.google.com/p/dart/issues/detail?id=7994: the range analysis gives a fixed rang…

tests/language/fixed_length_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.
+
+// Regression test for https://code.google.com/p/dart/issues/detail?id=7994.
+
+void main() {
+  Expect.equals(-1, foo());
+}
+
+void foo() {  
+  var list = new List<int>.fixedLength(1024);
+
+  for(int i = 0; i < list.length; i++) list[i] = -i;
+
+  for(int n = list.length; n > 1; n--) {
+    for(int i = 0; i < n - 1; i++) {
+      if (list[i] > list[i + 1]) {
+        return list[i + 1];
+      }
+    }
+  }
+}