Add a priority to source changes for assists and fixes

pkg/analyzer_plugin/lib/plugin/plugin.dart

 // Copyright (c) 2017, 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.
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/dart/analysis/byte_store.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart'
     show AnalysisDriverScheduler, PerformanceLog;
 import 'package:analyzer/src/dart/analysis/file_byte_store.dart';
 import 'package:analyzer/src/dart/analysis/file_state.dart';
@@ skipping 209 matching lines @@
    */
   CompletionGetSuggestionsResult handleCompletionGetSuggestions(
           Map<String, Object> parameters) =>
       new CompletionGetSuggestionsResult(
           -1, -1, const <CompletionSuggestion>[]);
 
   /**
    * Handle an 'edit.getAssists' request.
    */
   EditGetAssistsResult handleEditGetAssists(Map<String, Object> parameters) =>
-      new EditGetAssistsResult(const <SourceChange>[]);
+      new EditGetAssistsResult(const <PrioritizedSourceChange>[]);
 
   /**
    * Handle an 'edit.getAvailableRefactorings' request. Subclasses that override
    * this method in order to participate in refactorings must also override the
    * method [handleEditGetRefactoring].
    */
   EditGetAvailableRefactoringsResult handleEditGetAvailableRefactorings(
           Map<String, Object> parameters) =>
       new EditGetAvailableRefactoringsResult(const <RefactoringKind>[]);
 
@@ skipping 160 matching lines @@
       response = new Response(id,
           error: new RequestError(
               RequestErrorCode.PLUGIN_ERROR, exception.toString(),
               stackTrace: stackTrace.toString()));
     }
     if (response != null) {
       _channel.sendResponse(response);
     }
   }
 }