Add support for completion of case labels.

pkg/analysis_server/lib/src/services/completion/arglist_computer.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 services.completion.computer.dart.arglist;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol_server.dart' hide Element,
     ElementKind;
@@ skipping 118 matching lines @@
       finished = true;
       _addArgListSuggestion(declaration.functionExpression.parameters);
     }
   }
 
   @override
   void declaredFunctionTypeAlias(FunctionTypeAlias declaration) {
   }
 
   @override
-  void declaredLabel(Label label) {
+  void declaredLabel(Label label, bool isCaseLabel) {
   }
 
   @override
   void declaredLocalVar(SimpleIdentifier name, TypeName type) {
   }
 
   @override
   void declaredMethod(MethodDeclaration declaration) {
     SimpleIdentifier selector = declaration.name;
     if (selector != null && name == selector.name) {
@@ skipping 56 matching lines @@
       if (id != null) {
         String name = id.name;
         if (name != null && name.length > 0) {
           return name;
         }
       }
     }
     return 'dynamic';
   }
 }