Analyze locals in await for loops as inside a try-finally.

tests/language/await_for_use_local_test.dart

+// Copyright (c) 2015, 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.
+
+import "dart:async";
+import "package:expect/expect.dart";
+import "package:async_helper/async_helper.dart";
+
+sumStream(s) async {
+  int accum = 0;
+  await for (var v in s) {
+    accum += v;
+  }
+  return accum;
+}
+
+test() async {
+  var countStreamController;
+  int i = 0;
+  void tick() {
+    if (i < 10) {
+      countStreamController.add(i);
+      i++;
+      scheduleMicrotask(tick);
+    } else {
+      countStreamController.close();
+    }
+  }
+
+  countStreamController = new StreamController(
+      onListen: () {
+        scheduleMicrotask(tick);
+      });
+  Expect.equals(45, await sumStream(countStreamController.stream));
+}
+
+void main() {
+  asyncStart();
+  test().then((_) => asyncEnd());
+}