Fix convergence issues in range analysis.

tests/language/range_analysis_test.dart

+// Copyright (c) 2012, 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.
+// Dart test program for constructors and initializers.
+
+// Checks that range analysis does not enter infinite loop trying to propagate
+// ranges through dependant phis.
+
+test() {
+  var sum = 0;
+  for (var i = 0; i < 10; i++) {
+    for (var j = i - 1; j >= 0; j--) {
+      for (var k = j; k < i; k++) {
+        sum += (i + j + k);
+      }
+    }
+  }
+  return sum;
+}
+
+main() {
+  for (var i = 0; i < 1000; i++) test();
+}