Fix bad assumption of environment builder when it comes to nested loops: blocks inside a loop would…

tests/language/bailout4_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.
+
+// Test that dart2s computes the right bailout environment in presence
+// of nested loops.
+
+class A {
+  operator[] (index) => 42;
+}
+
+var a = new A();
+var b = new List(4);
+int count = 0;
+
+main() {
+  // Make the method recursive to make sure it gets an optimized
+  // version.
+  if (b[0] != null) main();
+
+  for (int i = 0; i < 2; i++) {
+    for (int j = 0; j < 2; j++) {
+      for (int k = 0; k < 2; k++) {
+        Expect.equals(42, a[i + j + k]);
+        count++;
+      }
+    }
+  }
+  Expect.equals(8, count);
+}