Add a "Label" Node around an Identifier that is being used as a label.

lib/compiler/implementation/ssa/builder.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.
 
 class Interceptors {
   Compiler compiler;
   Interceptors(Compiler this.compiler);
 
   SourceString mapOperatorToMethodName(Operator op) {
     String name = op.source.stringValue;
@@ skipping 2797 matching lines @@
         VariableDefinitions variableDefinitions = node.declaredIdentifier;
         variable = elements[variableDefinitions.definitions.nodes.head];
       }
       localsHandler.updateLocal(variable, pop());
 
       visit(node.body);
     }
     handleLoop(node, buildInitializer, buildCondition, () {}, buildBody);
   }
 
+  visitLabel(Label node) {
+    compiler.internalError('SsaBuilder.visitLabel', node: node);
+  }
+
   visitLabeledStatement(LabeledStatement node) {
     Statement body = node.getBody();
     if (body is Loop || body is SwitchStatement) {
       // Loops and switches handle their own labels.
       visit(body);
       return;
     }
     // Non-loop statements can only be break targets, not continue targets.
     TargetElement targetElement = elements[body];
     if (targetElement === null || targetElement.statement !== body) {
@@ skipping 488 matching lines @@
                                    <HInstruction>[target, input],
                                    HType.STRING));
     return builder.pop();
   }
 
   HInstruction result() {
     flushLiterals();
     return prefix;
   }
 }