Move HTTPParsers.cpp/.h to platform/

(Ignoring some small nits, fixed others)

BUG=297477
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/27043003

git-svn-id: svn://svn.chromium.org/blink/trunk@159528 bbb929c8-8fbe-4397-9dbb-9b2b20218538