Forget keys when we forget the volume.

Bug: 25861755
Test: create a volume, forget it, check logs and filesystem.
Change-Id: I0ab662969c51703cb046d57b72330e0f14447ef3
diff --git a/Ext4Crypt.h b/Ext4Crypt.h
index d0afd85..4226f15 100644
--- a/Ext4Crypt.h
+++ b/Ext4Crypt.h
@@ -16,12 +16,8 @@
 
 #include <string>
 
-#include <stdbool.h>
-#include <sys/cdefs.h>
-
 #include <cutils/multiuser.h>
 
-// General functions
 bool e4crypt_initialize_global_de();
 
 bool e4crypt_init_user0();
@@ -39,4 +35,6 @@
                                   int flags);
 bool e4crypt_destroy_user_storage(const std::string& volume_uuid, userid_t user_id, int flags);
 
+bool e4crypt_destroy_volume_keys(const std::string& volume_uuid);
+
 bool e4crypt_secdiscard(const std::string& path);