pkg/shelf: case-insensitive headers, cleaner Request ctor, a lot more tests

pkg/shelf/lib/src/response.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.response;
 
 import 'dart:async';
 import 'dart:convert';
 
-import 'package:collection/wrappers.dart';
 import 'package:http_parser/http_parser.dart';
 
 import 'message.dart';
 
 /// The response returned by a [Handler].
 class Response extends Message {
   /// The HTTP status code of the response.
   final int statusCode;
 
   /// The date and time after which the response's data should be considered
@@ skipping 193 matching lines @@
   if (body is String) return new Stream.fromIterable([encoding.encode(body)]);
   if (body is Stream) return body;
 
   throw new ArgumentError('Response body "$body" must be a String or a '
       'Stream.');
 }
 
 /// Adds information about [encoding] to [headers].
 ///
 /// Returns a new map without modifying [headers].
-UnmodifiableMapView<String, String> _adjustHeaders(
+Map<String, String> _adjustHeaders(
     Map<String, String> headers, Encoding encoding) {
   if (headers == null) headers = const {};
-  if (encoding == null) return new UnmodifiableMapView(headers);
+  if (encoding == null) return headers;
   if (headers['content-type'] == null) {
-    return new UnmodifiableMapView(_addHeader(headers, 'content-type',
-        'application/octet-stream; charset=${encoding.name}'));
+    return _addHeader(headers, 'content-type',
+        'application/octet-stream; charset=${encoding.name}');
   }
 
   var contentType = new MediaType.parse(headers['content-type'])
       .change(parameters: {'charset': encoding.name});
-  return new UnmodifiableMapView(
-      _addHeader(headers, 'content-type', contentType.toString()));
+  return _addHeader(headers, 'content-type', contentType.toString());
 }
 
 /// Adds a header with [name] and [value] to [headers], which may be null.
 ///
 /// Returns a new map without modifying [headers].
 Map<String, String> _addHeader(Map<String, String> headers, String name,
     String value) {
   headers = headers == null ? {} : new Map.from(headers);
   headers[name] = value;
   return headers;
@@ skipping 16 matching lines @@
 /// Converts [location], which may be a [String] or a [Uri], to a [String].
 ///
 /// Throws an [ArgumentError] if [location] isn't a [String] or a [Uri].
 String _locationToString(location) {
   if (location is String) return location;
   if (location is Uri) return location.toString();
 
   throw new ArgumentError('Response location must be a String or Uri, was '
       '"$location".');
 }