Extract constants into separate libarary.

pkg/analysis_server/test/analysis_server_test.dart

Index: pkg/analysis_server/test/analysis_server_test.dart
diff --git a/pkg/analysis_server/test/analysis_server_test.dart b/pkg/analysis_server/test/analysis_server_test.dart
index dd4807b72d4d4d7951935a84957271e7912b2b7c..85bcef1efbd7a1181287821617e4a9ab24bf5305 100644
--- a/pkg/analysis_server/test/analysis_server_test.dart
+++ b/pkg/analysis_server/test/analysis_server_test.dart
@@ -9,6 +9,7 @@ import 'dart:async';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analysis_server/src/analysis_server.dart';
+import 'package:analysis_server/src/constants.dart';
 import 'package:analysis_server/src/domain_server.dart';
 import 'package:analysis_server/src/protocol.dart';
 import 'package:analysis_server/src/resource.dart';
@@ -204,7 +205,7 @@ class AnalysisServerTest {
 
   static Future shutdown() {
     server.handlers = [new ServerDomainHandler(server)];
-    var request = new Request('my28', ServerDomainHandler.SHUTDOWN_METHOD);
+    var request = new Request('my28', METHOD_SHUTDOWN);
     return channel.sendRequest(request)
         .then((Response response) {
           expect(response.id, equals('my28'));