Add IRestoreSession interface for the restore flow

Restore is a fairly complicated, somewhat stateful process, so we introduce
a new interface to encapsulate the various bits and pieces into a nicely
separable component.  In particular, this will make it much cleaner to
open and interrogate an expensive-to-construct transport and then reuse it
for the actual restore process itself.
diff --git a/Android.mk b/Android.mk
index 26bcb5c..f50f58f 100644
--- a/Android.mk
+++ b/Android.mk
@@ -83,6 +83,7 @@
 	core/java/android/app/IWallpaperService.aidl \
 	core/java/android/app/IWallpaperServiceCallback.aidl \
 	core/java/android/backup/IBackupManager.aidl \
+	core/java/android/backup/IRestoreSession.aidl \
 	core/java/android/bluetooth/IBluetoothA2dp.aidl \
 	core/java/android/bluetooth/IBluetoothDevice.aidl \
 	core/java/android/bluetooth/IBluetoothDeviceCallback.aidl \