disable unpriv perf by default in user{,debug} builds

(Cherry picked from commit f2ac912b19ccbcc15d5176ec52c99744810adce7)

Bug: 29054680

Change-Id: If04bc63fc366006cde842a50b7c764f89d7449a6
diff --git a/core/main.mk b/core/main.mk
index 5b6e1e9..a6f829a 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -316,6 +316,7 @@
 ifneq (,$(user_variant))
   # Target is secure in user builds.
   ADDITIONAL_DEFAULT_PROPERTIES += ro.secure=1
+  ADDITIONAL_DEFAULT_PROPERTIES += security.perf_harden=1
 
   ifeq ($(user_variant),userdebug)
     # Pick up some extra useful tools