Fix scoping async functions.

tests/language/await_future_test.dart

 // Copyright (c) 2014, 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.
 
 // VMOptions=--enable_async --optimization-counter-threshold=5
 
 import 'package:expect/expect.dart';
 
 import 'dart:async';
 
@@ skipping 30 matching lines @@
       throw x;
     } catch (e1) {
       var y = await baz(e1 + 1);
       throw y;
     }
   } catch (e2) {
     return e2;
   }
 }
 
+nesting() async {
+  try {
+    try {
+      var x = 1;
+      var y = () async {
+        try {
+          var z = (await bar(3)) + x;
+          throw z;
+        }  catch (e1) {
+          return e1;
+        }
+      };
+      var a = await y();
+      throw a;
+    } catch (e2) {
+      throw e2 + 1;
+    }
+  } catch (e3) {
+    return e3;
+  }
+}
+
 main() async {
   var result;
   for (int i = 0; i < 10; i++) {
     result = await foo();
     Expect.equals(result, 30);
     result = await quaz(17);
     Expect.equals(result, 17);
     result = await quazz();
     Expect.equals(result, 2);
+    result = await nesting();
+    Expect.equals(result, 5);
   }
 }