Make sure all loop-phis are declared.

tests/language/recursive_loop_phis_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.
+
+// This program tripped dart2js.
+
+foo(bool b) {
+  var x = 499;
+  // If the loop-phi is not declared it will assign to a global and the
+  // recursive call will screw up the methods "local" state.
+  for (int i = 0; i < 3; i++) {
+    if (i == 0 && b) x = 42;
+    if (!b) foo(true);
+  }
+  return x;
+}
+
+main() {
+  Expect.equals(499, foo(false));
+}
+