Fix bad mangling of environment parameters.

tests/language/state_mangling3_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.
 
-foo(state) {
-  if (state == null) return 0;
+foo(state0) {
+  if (state0 == null) return 0;
   var sum = 0;
-  for (int i = 0; i < state.length; i++) {
-    sum += state[i];
+  for (int i = 0; i < state0.length; i++) {
+    sum += state0[i];
   }
-  state = inscrutableId(state);
-  for (int i = 0; i < state.length; i++) {
-    sum += state[i];
+  state0 = inscrutableId(state0);
+  for (int i = 0; i < state0.length; i++) {
+    sum += state0[i];
   }
   return sum;
 }
 
 int inscrutable(int x) => x == 0 ? 0 : x | inscrutable(x & (x - 1));
 
 inscrutableId(x) {
   if (x == 0) return inscrutable(x);
   return (3 == inscrutable(3)) ? x : false;
 }
 
 class A {
   int length = 3;
   operator [](i) => 1;
 }
 
 main() {
   Expect.equals(12, foo([1, 2, 3]));
   if (inscrutableId(0) == 0) {
     Expect.equals(6, foo(new A()));
   }
 }