Make AssistContributor asynchronous.

pkg/analysis_server/lib/src/edit/edit_domain.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 edit.domain;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/plugin/edit/fix/fix_core.dart';
@@ skipping 112 matching lines @@
       newStart = 0;
     }
     if (newLength == null) {
       newLength = 0;
     }
 
     return new EditFormatResult(edits, newStart, newLength)
         .toResponse(request.id);
   }
 
-  Response getAssists(Request request) {
+  Future getAssists(Request request) async {
     EditGetAssistsParams params = new EditGetAssistsParams.fromRequest(request);
     ContextSourcePair pair = server.getContextSourcePair(params.file);
     engine.AnalysisContext context = pair.context;
     Source source = pair.source;
     List<SourceChange> changes = <SourceChange>[];
     if (context != null && source != null) {
-      List<Assist> assists = computeAssists(
+      List<Assist> assists = await computeAssists(
           server.serverPlugin, context, source, params.offset, params.length);
       assists.forEach((Assist assist) {
         changes.add(assist.change);
       });
     }
-    return new EditGetAssistsResult(changes).toResponse(request.id);
+    Response response =
+        new EditGetAssistsResult(changes).toResponse(request.id);
+    server.sendResponse(response);
   }
 
   Response getFixes(Request request) {
     var params = new EditGetFixesParams.fromRequest(request);
     String file = params.file;
     int offset = params.offset;
     // add fixes
     List<AnalysisErrorFixes> errorFixesList = <AnalysisErrorFixes>[];
     List<CompilationUnit> units = server.getResolvedCompilationUnits(file);
     for (CompilationUnit unit in units) {
@@ skipping 24 matching lines @@
     return new EditGetFixesResult(errorFixesList).toResponse(request.id);
   }
 
   @override
   Response handleRequest(Request request) {
     try {
       String requestName = request.method;
       if (requestName == EDIT_FORMAT) {
         return format(request);
       } else if (requestName == EDIT_GET_ASSISTS) {
-        return getAssists(request);
+        getAssists(request);
+        return Response.DELAYED_RESPONSE;
       } else if (requestName == EDIT_GET_AVAILABLE_REFACTORINGS) {
         return _getAvailableRefactorings(request);
       } else if (requestName == EDIT_GET_FIXES) {
         return getFixes(request);
       } else if (requestName == EDIT_GET_REFACTORING) {
         return _getRefactoring(request);
       } else if (requestName == EDIT_ORGANIZE_DIRECTIVES) {
         return organizeDirectives(request);
       } else if (requestName == EDIT_SORT_MEMBERS) {
         return sortMembers(request);
@@ skipping 534 matching lines @@
     }
     return new RefactoringStatus();
   }
 }
 
 /**
  * [_RefactoringManager] throws instances of this class internally to stop
  * processing in a manager that was reset.
  */
 class _ResetError {}