Add 'Server' and 'User-Agent' default header fields.

They include the major and minor version of Dart.

BUG=
R=sgjesse@google.com

Review URL: https://codereview.chromium.org//16758008

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/http@23844 260f80e4-7a28-3924-810f-c04153c831b5
3 files changed
tree: 895c7de6cbb5c0eceb3e80dddd3094673716da38
  1. lib/
  2. test/
  3. pubspec.yaml