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

device/bluetooth/bluetooth_adapter_unittest.cc

Index: device/bluetooth/bluetooth_adapter_unittest.cc
diff --git a/device/bluetooth/bluetooth_adapter_unittest.cc b/device/bluetooth/bluetooth_adapter_unittest.cc
index 81e2dcbfdad263c7e8a24db571fd214e4a956929..939ae0509fd37521dfea73a7c5f431993e346c31 100644
--- a/device/bluetooth/bluetooth_adapter_unittest.cc
+++ b/device/bluetooth/bluetooth_adapter_unittest.cc
@@ -19,10 +19,6 @@ class TestBluetoothAdapter : public BluetoothAdapter {
   TestBluetoothAdapter() {
   }
 
-  void AddObserver(BluetoothAdapter::Observer* observer) override {}
-
-  void RemoveObserver(BluetoothAdapter::Observer* observer) override {}
-
   std::string GetAddress() const override { return ""; }
 
   std::string GetName() const override { return ""; }