Reapply "Fix URI encoding/decoding of + and space""

Updated test expectations for some tests for pkg/http, pkg/oauth2 and
pub to match the change.

TBR=lrn@google.com

Review URL: https://codereview.chromium.org//11659009

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@16426 260f80e4-7a28-3924-810f-c04153c831b5