Convert ErrorCallback to a OnceCallback in BluetoothGattCharacteristic

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=avi@chromium.org, hansberry@chromium.org, kpaulhamus@chromium.org, reillyg@chromium.org
TBR=avi

Bug: 953861
Change-Id: I2216e4003d7fe569f69e97c5b471baf49228950d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1584700
Commit-Queue: danakj <danakj@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Reviewed-by: Kim Paulhamus <kpaulhamus@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654232}
29 files changed