Add assist to convert part-of directives

pkg/analysis_server/test/services/correction/assist_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 'dart:async';
 
 import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/plugin/edit/assist/assist_dart.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
 import 'package:analysis_server/src/services/correction/assist.dart';
@@ skipping 1024 matching lines @@
     body: new Center(
       /*caret*/children: <Widget>[new GestureDetector()],
       key: null,
     ),
 // end
   );
 }
 ''');
   }
 
+  test_convertPartOfToUri_file_nonSibling() async {
+    addSource('/pkg/lib/foo.dart', '''
+library foo;
+part 'src/bar.dart';
+''');
+    testFile = provider.convertPath('/pkg/lib/src/bar.dart');
+    await resolveTestUnit('''
+part of foo;
+''');
+    await assertHasAssistAt('foo', DartAssistKind.CONVERT_PART_OF_TO_URI, '''
+part of '../foo.dart';
+''');
+  }
+
+  test_convertPartOfToUri_file_sibling() async {
+    addSource('/pkg/foo.dart', '''
+library foo;
+part 'bar.dart';
+''');
+    testFile = provider.convertPath('/pkg/bar.dart');
+    await resolveTestUnit('''
+part of foo;
+''');
+    await assertHasAssistAt('foo', DartAssistKind.CONVERT_PART_OF_TO_URI, '''
+part of 'foo.dart';
+''');
+  }
+
   test_convertToBlockBody_BAD_noEnclosingFunction() async {
     await resolveTestUnit('''
 var v = 123;
 ''');
     await assertNoAssistAt('v =', DartAssistKind.CONVERT_INTO_BLOCK_BODY);
   }
 
   test_convertToBlockBody_BAD_notExpressionBlock() async {
     await resolveTestUnit('''
 fff() {
@@ skipping 3318 matching lines @@
 
   @override
   final AstProvider astProvider;
 
   @override
   final CompilationUnit unit;
 
   _DartAssistContextForValues(this.source, this.selectionOffset,
       this.selectionLength, this.analysisDriver, this.astProvider, this.unit);
 }