implement LabeledStatement and Break in kernel

pkg/compiler/lib/src/ssa/locals_handler.dart

 // Copyright (c) 2016, 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 '../closure.dart';
 import '../common.dart';
 import '../compiler.dart' show Compiler;
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../io/source_information.dart';
@@ skipping 557 matching lines @@
   }
 
   /// When control flow merges, this method can be used to merge several
   /// localsHandlers into a new one using phis.  The new localsHandler is
   /// returned.  Unless it is also in the list, the current localsHandler is not
   /// used for its values, only for its declared variables. This is a way to
   /// exclude local values from the result when they are no longer in scope.
   LocalsHandler mergeMultiple(
       List<LocalsHandler> localsHandlers, HBasicBlock joinBlock) {
     assert(localsHandlers.length > 0);
-    if (localsHandlers.length == 1) return localsHandlers[0];
+    if (localsHandlers.length == 1) return localsHandlers.single;
     Map<Local, HInstruction> joinedLocals = new Map<Local, HInstruction>();
     HInstruction thisValue = null;
     directLocals.forEach((Local local, HInstruction instruction) {
       if (local != closureData.thisLocal) {
         HPhi phi = new HPhi.noInputs(local, commonMasks.dynamicType);
         joinedLocals[local] = phi;
         joinBlock.addPhi(phi);
       } else {
         // We know that "this" never changes, if it's there.
         // Save it for later. While merging, there is no phi for "this",
@@ skipping 74 matching lines @@
   final ExecutableElement executableContext;
 
   // Avoid slow Object.hashCode.
   final int hashCode = _nextHashCode = (_nextHashCode + 1).toUnsigned(30);
   static int _nextHashCode = 0;
 
   SyntheticLocal(this.name, this.executableContext);
 
   toString() => 'SyntheticLocal($name)';
 }