bluetooth: Initial IDL for navigator.bluetooth.

Intent to Implement, 2014-08-29
https://groups.google.com/a/chromium.org/d/topic/blink-dev/pfNeo5cFXCk/discussion
https://groups.google.com/a/chromium.org/d/msg/blink-dev/6B8fTZLq6x8/B9TDKOUxVNAJ

BUG=420275

Review URL: https://codereview.chromium.org/629493003

git-svn-id: svn://svn.chromium.org/blink/trunk@183234 bbb929c8-8fbe-4397-9dbb-9b2b20218538