Use TypeSystem in the 'Extract Method' refactoring.

pkg/analysis_server/lib/src/services/refactoring/extract_method.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 services.src.refactoring.extract_method;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/name_suggestion.dart';
@@ skipping 576 matching lines @@
     }
     // verify that none or all execution flows end with a "return"
     if (_selectionStatements != null) {
       bool hasReturn = _selectionStatements.any(_mayEndWithReturnStatement);
       if (hasReturn && !ExitDetector.exits(_selectionStatements.last)) {
         result.addError(ERROR_EXITS);
       }
     }
     // maybe ends with "return" statement
     if (_selectionStatements != null) {
-      _ReturnTypeComputer returnTypeComputer = new _ReturnTypeComputer();
+      _ReturnTypeComputer returnTypeComputer = new _ReturnTypeComputer(context);
       _selectionStatements.forEach((statement) {
         statement.accept(returnTypeComputer);
       });
       _returnType = returnTypeComputer.returnType;
     }
     // maybe single variable to return
     if (assignedUsedVariables.length == 1) {
       // we cannot both return variable and have explicit return statement
       if (_returnType != null) {
         result.addFatalError(
@@ skipping 543 matching lines @@
 class _Occurrence {
   final SourceRange range;
   final bool isSelection;
 
   Map<String, String> _parameterOldToOccurrenceName = <String, String>{};
 
   _Occurrence(this.range, this.isSelection);
 }
 
 class _ReturnTypeComputer extends RecursiveAstVisitor {
+  final AnalysisContext context;
+
   DartType returnType;
 
+  _ReturnTypeComputer(this.context);
+
   @override
   visitBlockFunctionBody(BlockFunctionBody node) {}
 
   @override
   visitReturnStatement(ReturnStatement node) {
     // prepare expression
     Expression expression = node.expression;
     if (expression == null) {
       return;
     }
     // prepare type
     DartType type = expression.bestType;
     if (type.isBottom) {
       return;
     }
     // combine types
     if (returnType == null) {
       returnType = type;
     } else {
       if (returnType is InterfaceType && type is InterfaceType) {
         returnType = InterfaceType.getSmartLeastUpperBound(returnType, type);
       } else {
-        returnType = returnType.getLeastUpperBound(type);
+        returnType = context.typeSystem
+            .getLeastUpperBound(context.typeProvider, returnType, type);
       }
     }
   }
 }
 
 /**
  * Generalized version of some source, in which references to the specific
  * variables are replaced with pattern variables, with back mapping from the
  * pattern to the original variable names.
  */
@@ skipping 10 matching lines @@
       return false;
     }
     for (int i = 0; i < parameterTypes.length; i++) {
       if (other.parameterTypes[i] != parameterTypes[i]) {
         return false;
       }
     }
     return true;
   }
 }