Delay touching disks when secure keyguard showing.

We've tried our best to protect against malicious storage devices
with limited SELinux domains, but let's be even more paranoid and
refuse to look at disks inserted while a secure keyguard is
showing.  We'll gladly scan them right away once the user confirms
their credentials.

Test: builds, boots, manual testing
Bug: 68054513
Change-Id: I37fd6c25bbd6631fa4ba3f84e19384d746a22498
diff --git a/binder/android/os/IVold.aidl b/binder/android/os/IVold.aidl
index c3f5029..d073be2 100644
--- a/binder/android/os/IVold.aidl
+++ b/binder/android/os/IVold.aidl
@@ -33,6 +33,8 @@
     void onUserStarted(int userId);
     void onUserStopped(int userId);
 
+    void onSecureKeyguardStateChanged(boolean isShowing);
+
     void partition(@utf8InCpp String diskId, int partitionType, int ratio);
     void forgetPartition(@utf8InCpp String partGuid, @utf8InCpp String fsUuid);