more progress implementing analysis server code completion

pkg/analysis_server/lib/src/computer/computer_overrides.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 computer.overrides;
 
-import 'package:analysis_server/src/collections.dart';
 import 'package:analysis_server/src/computer/element.dart';
-import 'package:analysis_server/src/constants.dart';
+import 'package:analysis_services/constants.dart';
+import 'package:analysis_services/json.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart' as engine;
 
 
 /**
  * A computer for class member overrides in a Dart [CompilationUnit].
  */
 class DartUnitOverridesComputer {
   final CompilationUnit _unit;
 
@@ skipping 131 matching lines @@
       json[INTERFACE_ELEMENTS] = interfaceElements.map((element) {
         return element.toJson();
       }).toList();
     }
     return json;
   }
 
   @override
   String toString() => toJson().toString();
 }