Migrate chrome.bluetooth API backend to use device::BluetoothDiscoverySession.

device/bluetooth/bluetooth_discovery_session.h

Index: device/bluetooth/bluetooth_discovery_session.h
diff --git a/device/bluetooth/bluetooth_discovery_session.h b/device/bluetooth/bluetooth_discovery_session.h
index bc2f89305cefb5c768baecb21fc829c45ac3c0fc..666538b8e060487b2af38946e485fc282f0a1ec6 100644
--- a/device/bluetooth/bluetooth_discovery_session.h
+++ b/device/bluetooth/bluetooth_discovery_session.h
@@ -58,10 +58,12 @@ class BluetoothDiscoverySession {
                     const ErrorCallback& error_callback);
 
  protected:
-  friend class BluetoothAdapter;
-  explicit BluetoothDiscoverySession(BluetoothAdapter* adapter);
+  BluetoothDiscoverySession();  // Called by mock.
 
  private:
+  friend class BluetoothAdapter;
+  explicit BluetoothDiscoverySession(scoped_refptr<BluetoothAdapter> adapter);
+
   // Internal callback invoked when a call to Stop has succeeded.
   void OnStop(const base::Closure& callback);