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 ConnectionCallback(const BluetoothDevice *device,
                          scoped_refptr<BluetoothSocket> socket) {
    ++connection_callback_count_;
    last_device_ = device;
    last_socket_ = socket;

    message_loop_.Quit();
  }

  void ConnectionCallback(const BluetoothDevice *device,
                          scoped_refptr<BluetoothSocket> socket) {
    ++connection_callback_count_;
    last_device_ = device;
    last_socket_ = socket;

    message_loop_.Quit();
  }
