Test that plaintext can't be read from disk for encrypted files.

Bug: 36029169
Test: tested by hand on Taimen
Change-Id: I5717a8630bb2c8d8fe5c343d519c4e59862ecbdf
diff --git a/binder/android/os/IVold.aidl b/binder/android/os/IVold.aidl
index 32d9b16..5d182c9 100644
--- a/binder/android/os/IVold.aidl
+++ b/binder/android/os/IVold.aidl
@@ -40,6 +40,7 @@
     void unmount(@utf8InCpp String volId);
     void format(@utf8InCpp String volId, @utf8InCpp String fsType);
     void benchmark(@utf8InCpp String volId, IVoldTaskListener listener);
+    void checkEncryption(@utf8InCpp String volId);
 
     void moveStorage(@utf8InCpp String fromVolId, @utf8InCpp String toVolId,
             IVoldTaskListener listener);