Make server forward getNavigation requests to plugins

pkg/analysis_server/test/analysis/get_navigation_test.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.
 
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/domain_analysis.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:test/test.dart';
@@ skipping 26 matching lines @@
 main() {
   var test = 0;
   print(test);
 }
 ''');
     await _getNavigation(testFile, testCode.indexOf('test);'), 0);
     assertHasRegion('test);');
     assertHasTarget('test = 0');
   }
 
-  test_fileDoesNotExist() {
+  test_fileDoesNotExist() async {
     String file = '$projectPath/doesNotExist.dart';
-    return _checkInvalid(file, -1, -1);
+    Request request = _createGetNavigationRequest(file, 0, 100);
+    Response response = await serverChannel.sendRequest(request);
+    expect(response.error, isNull);
+    expect(response.result['files'], isEmpty);
+    expect(response.result['targets'], isEmpty);
+    expect(response.result['regions'], isEmpty);
   }
 
   test_fileOutsideOfRoot() async {
     testFile = '/outside.dart';
     addTestFile('''
 main() {
   var test = 0;
   print(test);
 }
 ''');
@@ skipping 161 matching lines @@
   var test = 0;
   print(test);
 }
 ''');
     await waitForTasksFinished();
     await _getNavigation(testFile, testCode.indexOf('test);'), 0);
     assertHasRegion('test);');
     assertHasTarget('test = 0');
   }
 
-  _checkInvalid(String file, int offset, int length) async {
-    Request request = _createGetNavigationRequest(file, offset, length);
-    Response response = await serverChannel.sendRequest(request);
-    expect(response.error, isNotNull);
-    expect(response.error.code, RequestErrorCode.GET_NAVIGATION_INVALID_FILE);
-  }
-
   Request _createGetNavigationRequest(String file, int offset, int length) {
     return new AnalysisGetNavigationParams(file, offset, length)
         .toRequest(requestId);
   }
 
   _getNavigation(String file, int offset, int length) async {
     Request request = _createGetNavigationRequest(file, offset, length);
     Response response = await serverChannel.sendRequest(request);
     AnalysisGetNavigationResult result =
         new AnalysisGetNavigationResult.fromResponse(response);
     targetFiles = result.files;
     targets = result.targets;
     regions = result.regions;
   }
 }