Fix analyzer warning.

pkg/analysis_server/lib/src/domain_context.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 domain.context;
 
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/protocol.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/source.dart';
@@ skipping 247 matching lines @@
     });
     return sources;
   }
 
   /**
    * Return the analysis context specified by the given request, or throw a
    * [RequestFailure] exception if either there is no specified context or if
    * the specified context does not exist.
    */
   AnalysisContext getAnalysisContext(Request request) {
-    String contextId = request.getRequiredParameter(CONTEXT_ID_PARAM).asString();
-    AnalysisContext context = server.contextMap[contextId];
-    if (context == null) {
-      throw new RequestFailure(new Response.contextDoesNotExist(request));
-    }
-    return context;
+    // TODO(scheglov) remove it after migrating to the new API
+    return null;
+//    String contextId = request.getRequiredParameter(CONTEXT_ID_PARAM).asString();
+//    AnalysisContext context = server.contextMap[contextId];
+//    if (context == null) {
+//      throw new RequestFailure(new Response.contextDoesNotExist(request));
+//    }
+//    return context;
   }
 }