Refactor to support default Bluetooth pairing delegate

In order to support a default pairing delegate we need to move the agent
service provider delegate implementation from BluetoothDevice to
BluetoothAdapter while retaining the existing API.

BUG=338492
TEST=device_unittests, unit_tests, browser_tests

Review URL: https://codereview.chromium.org/148293003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252216 0039d316-1c4b-4281-b951-d872f2087c98
void BluetoothDeviceChromeOS::RequestPinCode(

void BluetoothDeviceChromeOS::RequestPinCode(
    const dbus::ObjectPath& device_path,
    const PinCodeCallback& callback) {
  DCHECK(agent_.get());
  DCHECK(device_path == object_path_);
  VLOG(1) << object_path_.value() << ": RequestPinCode";
  UMA_HISTOGRAM_ENUMERATION("Bluetooth.PairingMethod",
                            UMA_PAIRING_METHOD_REQUEST_PINCODE,
                            UMA_PAIRING_METHOD_COUNT);
  DCHECK(pairing_delegate_);
  DCHECK(pincode_callback_.is_null());
  pincode_callback_ = callback;
  pairing_delegate_->RequestPinCode(this);
  pairing_delegate_used_ = true;
}
