Content-Type header is now stored with a case insensitive key.

pkg/http/lib/src/base_request.dart

Index: pkg/http/lib/src/base_request.dart
diff --git a/pkg/http/lib/src/base_request.dart b/pkg/http/lib/src/base_request.dart
index f54e757f0a6a6531afbccf2c5c10b72c5a0f53e2..7e5347b19f35317f86556baa5ea3a123d7323779 100644
--- a/pkg/http/lib/src/base_request.dart
+++ b/pkg/http/lib/src/base_request.dart
@@ -1,10 +1,11 @@
-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// 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 base_request;
 
 import 'dart:async';
+import 'dart:collection';
 
 import 'byte_stream.dart';
 import 'client.dart';
@@ -79,7 +80,9 @@ abstract class BaseRequest {
 
   /// Creates a new HTTP request.
   BaseRequest(this.method, this.url)
-    : headers = <String, String>{};
+    : headers = new LinkedHashMap<String, String>(
+        equals: (key1, key2) => key1.toLowerCase() == key2.toLowerCase(),
+        hashCode: (key) => key.toLowerCase().hashCode);
 
   /// Finalizes the HTTP request in preparation for it being sent. This freezes
   /// all mutable fields and returns a single-subscription [ByteStream] that