Enable proguard

Change-Id: I5a9fb731633ced3aa415b95d44fe2995981c9a52
diff --git a/Android.mk b/Android.mk
index a75ece8..20d7357 100644
--- a/Android.mk
+++ b/Android.mk
@@ -29,9 +29,7 @@
 LOCAL_RESOURCE_DIR := $(LOCAL_PATH)/res
 LOCAL_AAPT_FLAGS := --auto-add-overlay
 
-# TODO (ywen): Temporarily disabled. Turn it on before ship
-#LOCAL_PROGUARD_FLAG_FILES := proguard.cfg
-LOCAL_PROGUARD_ENABLED := disabled
+LOCAL_PROGUARD_FLAG_FILES := proguard.flags
 
 LOCAL_CERTIFICATE := platform
 LOCAL_PRIVILEGED_MODULE := true