GitLab

Fix for: https://codereview.chromium.org/1950033002/

Adding initial remote characteristic implementation on OS X, with only the basic methods (e.g. GetUUID) implemented.
Characteristic discovery also implemented in BluetoothRemoteGattServiceMac.

BUG=609064

Review-Url: https://codereview.chromium.org/2071323002
Cr-Commit-Position: refs/heads/master@{#400663}