Add optional tags to dalvik.

Change-Id: I29a78ccb6312d12b3ef0ed02cfbc638a5b01db9c
diff --git a/dx/src/Android.mk b/dx/src/Android.mk
index 7ab32b2..80d1b85 100644
--- a/dx/src/Android.mk
+++ b/dx/src/Android.mk
@@ -11,7 +11,7 @@
 
 LOCAL_SRC_FILES := $(call all-subdir-java-files)
 LOCAL_JAR_MANIFEST := ../etc/manifest.txt
-
+LOCAL_MODULE_TAGS := optional
 LOCAL_MODULE:= dx
 
 include $(BUILD_HOST_JAVA_LIBRARY)
@@ -25,7 +25,7 @@
 include $(CLEAR_VARS)
 
 LOCAL_SRC_FILES := $(call all-subdir-java-files) $(call all-subdir-html-files)
-
+LOCAL_MODULE_TAGS := optional
 LOCAL_MODULE:= dx
 LOCAL_DROIDDOC_OPTIONS := -hidden
 LOCAL_MODULE_CLASS := JAVA_LIBRARIES