dart2js cps: Support sync* and yield.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.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.
 
 library dart2js.ir_nodes_sexpr;
 
 import '../constants/values.dart';
 import '../util/util.dart';
 import 'cps_ir_nodes.dart';
 import '../universe/call_structure.dart' show
@@ skipping 349 matching lines @@
   }
 
   @override
   String visitAwait(Await node) {
     String value = access(node.input);
     String continuation = access(node.continuation);
     return '(Await $value $continuation)';
   }
 
   @override
+  String visitYield(Yield node) {
+    String value = access(node.input);
+    String continuation = access(node.continuation);
+    return '(Yield $value $continuation)';
+  }
+
   String visitRefinement(Refinement node) {
     String value = access(node.value);
     return '(Refinement $value ${node.type})';
   }
 }
 
 class ConstantStringifier extends ConstantValueVisitor<String, Null> {
   // Some of these methods are unimplemented because we haven't had a need
   // to print such constants.  When printing is implemented, the corresponding
   // parsing support should be added to SExpressionUnstringifier.parseConstant
@@ skipping 98 matching lines @@
   void setReturnContinuation(Continuation node) {
     assert(!_names.containsKey(node) || _names[node] == 'return');
     _names[node] = 'return';
   }
 
   String getName(Node node) {
     if (!_names.containsKey(node)) return 'MISSING_NAME';
     return _names[node];
   }
 }