Fix issue 12023 by avoiding a critical edge in the SSA graph with a switch statement.

sdk/lib/_internal/compiler/implementation/ssa/nodes.dart

 // Copyright (c) 2012, 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.
 
 part of ssa;
 
 abstract class HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBailoutTarget(HBailoutTarget node);
   R visitBitAnd(HBitAnd node);
@@ skipping 2677 matching lines @@
   bool accept(HStatementInformationVisitor visitor) =>
     visitor.visitTryInfo(this);
 }
 
 
 
 class HSwitchBlockInformation implements HStatementInformation {
   final HExpressionInformation expression;
   final List<List<Constant>> matchExpressions;
   final List<HStatementInformation> statements;
-  // If the switch has a default, it's the last statement block, which
-  // may or may not have other expresions.
-  final bool hasDefault;
   final TargetElement target;
   final List<LabelElement> labels;
 
   HSwitchBlockInformation(this.expression,
                           this.matchExpressions,
                           this.statements,
-                          this.hasDefault,
                           this.target,
                           this.labels);
 
   HBasicBlock get start => expression.start;
   HBasicBlock get end {
     // We don't create a switch block if there are no cases.
     assert(!statements.isEmpty);
     return statements.last.end;
   }
 
   bool accept(HStatementInformationVisitor visitor) =>
       visitor.visitSwitchInfo(this);
 }