Support Request hijacking in Shelf, using a similar API to Rack.

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';
@@ skipping 40 matching lines @@
       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'));
   });
+
+  test("doesn't log a HijackException", () {
+    var handler = const Pipeline()
+        .addMiddleware(logRequests(logger: logger))
+        .addHandler((request) => throw const HijackException());
+
+    expect(makeSimpleRequest(handler).whenComplete(() {
+      expect(gotLog, isFalse);
+    }), throwsA(new isInstanceOf<HijackException>()));
+  });
 }