Add optional tags to frameworks/base ext.

Change-Id: I08a69b7ca783994e52f735ad0ee9b85197cdaa96
diff --git a/Android.mk b/Android.mk
index 06a589c..566b36f 100644
--- a/Android.mk
+++ b/Android.mk
@@ -604,7 +604,7 @@
 
 LOCAL_NO_STANDARD_LIBRARIES := true
 LOCAL_JAVA_LIBRARIES := core
-
+LOCAL_MODULE_TAGS := optional
 LOCAL_MODULE := ext
 
 LOCAL_NO_EMMA_INSTRUMENT := true