dart2js: Bugfix for when 'await' occurs in an initializer list.

tests/compiler/dart2js/async_await_js_transform_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 "package:expect/expect.dart";
 import "package:compiler/src/js/js.dart";
 import "package:compiler/src/js/rewrite_async.dart";
 import "package:compiler/src/js_backend/js_backend.dart" show StringBackedName;
 
 void testTransform(String source, String expected, AsyncRewriterBase rewriter) {
@@ skipping 46 matching lines @@
   var __goto = 0, __completer = new Completer(), __handler = 1, __currentError, closures, v0, v1, v2, v3;
   var body = _wrapJsFunctionForAsync(function(__errorCode, __result) {
     if (__errorCode === 1) {
       __currentError = __result;
       __goto = __handler;
     }
     while (true)
       switch (__goto) {
         case 0:
           // Function start
+          closures = [new A.main_closure()];
           __goto = 2;
-        closures = [new A.main_closure()];
-        return thenHelper(closures, body, __completer);
+          return thenHelper(closures, body, __completer);
         case 2:
           // returning from await.
-          v0 = __result, v1 = 0;
+          v0 = __result;
+          v1 = 0;
           if (v1 < 0 || v1 >= v0.length)
             H.ioore(v0, v1);
           else
             ;
           v2 = 4;
           v3 = 2;
           P.print(v0[v1].call$2(v2, v3));
           // implicit return
           return thenHelper(null, 0, __completer, null);
         case 1:
@@ skipping 1147 matching lines @@
             // return
             return endOfIteration();
           case 2:
             // rethrow
             return uncaughtError(__currentError);
         }
     };
   });
 }""");
 }