Provide default implementations for NotificationDelegate methods.

ash/system/chromeos/bluetooth/bluetooth_notification_controller.cc

Index: ash/system/chromeos/bluetooth/bluetooth_notification_controller.cc
diff --git a/ash/system/chromeos/bluetooth/bluetooth_notification_controller.cc b/ash/system/chromeos/bluetooth/bluetooth_notification_controller.cc
index e64bc77c707ba87f5c19709a9ea59266cff94791..146be2c43c8750807442bd216475b8f2deffe69d 100644
--- a/ash/system/chromeos/bluetooth/bluetooth_notification_controller.cc
+++ b/ash/system/chromeos/bluetooth/bluetooth_notification_controller.cc
@@ -58,12 +58,8 @@ class BluetoothPairingNotificationDelegate
   virtual ~BluetoothPairingNotificationDelegate();
 
   // message_center::NotificationDelegate overrides.
-  virtual void Display() override;
-  virtual void Error() override;
-  virtual void Close(bool by_user) override;
-  virtual bool HasClickedListener() override;
-  virtual void Click() override;
-  virtual void ButtonClick(int button_index) override;
+  void Close(bool by_user) override;
+  void ButtonClick(int button_index) override;
 
  private:
   // Buttons that appear in notifications.
@@ -93,12 +89,6 @@ BluetoothPairingNotificationDelegate::BluetoothPairingNotificationDelegate(
 BluetoothPairingNotificationDelegate::~BluetoothPairingNotificationDelegate() {
 }
 
-void BluetoothPairingNotificationDelegate::Display() {
-}
-
-void BluetoothPairingNotificationDelegate::Error() {
-}
-
 void BluetoothPairingNotificationDelegate::Close(bool by_user) {
   VLOG(1) << "Pairing notification closed. by_user = " << by_user;
   // Ignore notification closes generated as a result of pairing completion.
@@ -111,13 +101,6 @@ void BluetoothPairingNotificationDelegate::Close(bool by_user) {
     device->CancelPairing();
 }
 
-bool BluetoothPairingNotificationDelegate::HasClickedListener() {
-  return false;
-}
-
-void BluetoothPairingNotificationDelegate::Click() {
-}
-
 void BluetoothPairingNotificationDelegate::ButtonClick(int button_index) {
   VLOG(1) << "Pairing notification, button click: " << button_index;
   // If the device object still exists, send the appropriate response either