Service Worker: Cache.put() consumes request/response bodies

Per SW spec issue:
https://github.com/slightlyoff/ServiceWorker/issues/550

Cache.put() should throw if request/response bodies
are already used, and consume request body (if non-empty)
and response body.

BUG=430962

Review URL: https://codereview.chromium.org/708703002

git-svn-id: svn://svn.chromium.org/blink/trunk@185323 bbb929c8-8fbe-4397-9dbb-9b2b20218538