bluetooth: Refactor (Add|Remove)Observer impls into BluetoothAdapter.

device/bluetooth/bluetooth_adapter_chromeos.h

Index: device/bluetooth/bluetooth_adapter_chromeos.h
diff --git a/device/bluetooth/bluetooth_adapter_chromeos.h b/device/bluetooth/bluetooth_adapter_chromeos.h
index 055bafb940e06daec87248d8dc92e2d21c39598c..4254b8afcaa8658eb546e3c7501ede42692abc09 100644
--- a/device/bluetooth/bluetooth_adapter_chromeos.h
+++ b/device/bluetooth/bluetooth_adapter_chromeos.h
@@ -66,8 +66,6 @@ class DEVICE_BLUETOOTH_EXPORT BluetoothAdapterChromeOS
   // BluetoothAdapter:
   void Shutdown() override;
   void DeleteOnCorrectThread() const override;
-  void AddObserver(device::BluetoothAdapter::Observer* observer) override;
-  void RemoveObserver(device::BluetoothAdapter::Observer* observer) override;
   std::string GetAddress() const override;
   std::string GetName() const override;
   void SetName(const std::string& name,
@@ -353,9 +351,6 @@ class DEVICE_BLUETOOTH_EXPORT BluetoothAdapterChromeOS
   // Object path of the adapter we track.
   dbus::ObjectPath object_path_;
 
-  // List of observers interested in event notifications from us.
-  ObserverList<device::BluetoothAdapter::Observer> observers_;
-
   // Instance of the D-Bus agent object used for pairing, initialized with
   // our own class as its delegate.
   scoped_ptr<BluetoothAgentServiceProvider> agent_;