Fix problems with default-cases in async code.

pkg/compiler/lib/src/js/rewrite_async.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.
 
 library rewrite_async;
 
 import "dart:math" show max;
 import 'dart:collection';
 
 import 'package:_internal/compiler/js_lib/shared/async_await_error_codes.dart'
@@ skipping 1287 matching lines @@
         addGoto(labels[defaultIndex]);
       }
     } else {
       bool hasDefault = false;
       int i = 0;
       List<js.SwitchClause> clauses = new List<js.SwitchClause>();
       for (js.SwitchClause clause in node.cases) {
         if (clause is js.Case) {
           labels[i] = newLabel("case");
           clauses.add(new js.Case(clause.expression, gotoAndBreak(labels[i])));
-        } else if (i is js.Default) {
+        } else if (clause is js.Default) {
           labels[i] = newLabel("default");
           clauses.add(new js.Default(gotoAndBreak(labels[i])));
           hasDefault = true;
         } else {
           diagnosticListener.internalError(
               spannable, "Unknown clause type $clause");
         }
         i++;
       }
+      if (!hasDefault) {
+        clauses.add(new js.Default(gotoAndBreak(after)));
+      }
       withExpression(node.key, (js.Expression key) {
         addStatement(new js.Switch(key, clauses));
       }, store: false);
-      if (!hasDefault) {
-        addGoto(after);
-      }
+
+      addBreak();
     }
 
     jumpTargets.add(node);
     for (int i = 0; i < labels.length; i++) {
       beginLabel(labels[i]);
       visitStatement(node.cases[i].body);
     }
     beginLabel(after);
     jumpTargets.removeLast();
   }
@@ skipping 1117 matching lines @@
     return condition || body;
   }
 
   @override
   bool visitDartYield(js.DartYield node) {
     hasYield = true;
     visit(node.expression);
     return true;
   }
 }