Add utility methods for sending non-form data in pkg/http.
Add utility methods for sending non-form data in pkg/http.

R=rnystrom@google.com
BUG=8380

Review URL: https://codereview.chromium.org//65583004

git-svn-id: a962b240025cf0577aa172e20f49ccb159ba6be1@30183 260f80e4-7a28-3924-810f-c04153c831b5

dart-lang/pub,dart-lang/pub,computmaxer/pub,cjkao/dart-pub,maxwellpeterson-wf/pub