Add captive portal API.

This API allows apps other than the system's CaptivePortalLogin
to handle signing in to captive portals.

bug:19416463
Change-Id: I27fce5856b635233e6ff66396d50ccabedd76cf5
3 files changed
tree: 22d6e861743637eb2771e81b63f59eaf0cdf1854
  1. core/
  2. services/
  3. tests/