BluetoothProfile: re-register on adapter presence

Hold on to the copy of the BluetoothAdapter object and register as
an observer. If the adapter is removed for any reason, including a
bluetoothd crash, when it returns attempt to re-register the profile
again.

bluetooth_profile_manager::kErrorAlreadyExists only means that the
profile exists on this D-Bus connection, so this is a safe error
to ignore.

BUG=330278
TEST=restart bluetoothd while Chrome running

Review URL: https://codereview.chromium.org/195893003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256503 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256503