NSInputStream requires overriding and implementing private methods in order to
use it with NSURLConnection [1]. It is cleaner to use the private but stable
and open source CFStreamAbstract.h header from CF-Lite to implement a
CFReadStream. Since CFReadStream is toll-free bridged to NSInputStream, the
remainder of the HTTPTransport code can remain unchanged.
[1] http://lists.apple.com/archives/macnetworkprog/2007/May/msg00055.html
BUG=crashpad:15
R=mark@chromium.org
Review URL: https://codereview.chromium.org/993413003
