Mark Network Information as Stable.

See https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/sTtZIk4XkaY for intent to ship.

BUG=368358

Review URL: https://codereview.chromium.org/429883003

git-svn-id: svn://svn.chromium.org/blink/trunk@179308 bbb929c8-8fbe-4397-9dbb-9b2b20218538