bluetooth: Require frame to be connected for stopNotifications to succeed.
If a frame is not connected or disconnects during a stopNotifications
request we reject the promise with NetworkError.
Also adds a new adapter for delayed StopNotifySession callbacks.
BUG=
608538
Committed:
https://crrev.com/7a703abc1287ff478b1bfe15bf68af7b48331740
Cr-Commit-Position: refs/heads/master@{#428655}