pkg/shelf: rename Stack to Pipeline

pkg/shelf/test/log_middleware_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.
 
 library shelf.log_middleware_test;
 
 import 'package:shelf/shelf.dart';
 import 'package:unittest/unittest.dart';
 
 import 'test_util.dart';
 
 void main() {
   bool gotLog;
 
   setUp(() {
     gotLog = false;
   });
 
   var logger = (msg, isError) {
     expect(gotLog, isFalse);
     gotLog = true;
     expect(isError, isFalse);
     expect(msg, contains('GET'));
     expect(msg, contains('[200]'));
   };
 
   test('logs a request with a synchronous response', () {
-    var handler = const Stack()
+    var handler = const Pipeline()
         .addMiddleware(logRequests(logger: logger))
         .addHandler(syncHandler);
 
     return makeSimpleRequest(handler).then((response) {
       expect(gotLog, isTrue);
     });
   });
 
   test('logs a request with an asynchronous response', () {
-    var handler = const Stack()
+    var handler = const Pipeline()
         .addMiddleware(logRequests(logger: logger))
         .addHandler(asyncHandler);
 
     return makeSimpleRequest(handler).then((response) {
       expect(gotLog, isTrue);
     });
   });
 
   test('logs a request with an asynchronous response', () {
-    var handler = const Stack()
+    var handler = const Pipeline()
         .addMiddleware(logRequests(logger: (msg, isError) {
       expect(gotLog, isFalse);
       gotLog = true;
       expect(isError, isTrue);
       expect(msg, contains('\tGET\t/'));
       expect(msg, contains('testing logging throw'));
     })).addHandler((request) {
       throw 'testing logging throw';
     });
 
     expect(makeSimpleRequest(handler), throwsA('testing logging throw'));
   });
 }