Convert Callbacks to OnceCallbacks for errors in BluetoothGattDescriptor

This will allow us to convert more Callbacks in the bluetooth component
over to OnceCallbacks, which will let us convert Callbacks in content
eventually.

R=reillyg@chromium.org

Bug: 953861
Change-Id: Iaca0042c4b2ed5559a70c2136f20881546673406
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1574429
Auto-Submit: danakj <danakj@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653187}
28 files changed