Prepare for decoupling analyzer ASTs from element model.

pkg/analysis_server/lib/src/services/refactoring/extract_method.dart

Index: pkg/analysis_server/lib/src/services/refactoring/extract_method.dart
diff --git a/pkg/analysis_server/lib/src/services/refactoring/extract_method.dart b/pkg/analysis_server/lib/src/services/refactoring/extract_method.dart
index 107abf3d74f6ee955c2be1ef2056439a7fdeeb20..366f282a8aab0b8c235cc797722e7b8dba79fe3c 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/extract_method.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/extract_method.dart
@@ -21,6 +21,7 @@ import 'package:analysis_server/src/services/refactoring/rename_unit_member.dart
 import 'package:analysis_server/src/services/search/element_visitors.dart';
 import 'package:analysis_server/src/services/search/search_engine.dart';
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/standard_resolution_map.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
@@ -411,7 +412,8 @@ class ExtractMethodRefactoringImpl extends RefactoringImpl
     AstNode parent = _parentMember.parent;
     // top-level function
     if (parent is CompilationUnit) {
-      LibraryElement libraryElement = parent.element.library;
+      LibraryElement libraryElement =
+          resolutionMap.elementForCompilationUnit(parent).library;
       return validateCreateFunction(searchEngine, libraryElement, name);
     }
     // method of class