Add a tool to let you enforce layering between packages in a java module.

And build system support for it too.

Change-Id: I4dd5ed0b9edab6e8884b0d00cfeeae5fa38d967a
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 999bd73..e7edbf3 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -60,6 +60,7 @@
 LOCAL_INTERMEDIATE_SOURCE_DIR:=
 LOCAL_JAVACFLAGS:=
 LOCAL_JAVA_LIBRARIES:=
+LOCAL_JAVA_LAYERS_FILE:=
 LOCAL_NO_STANDARD_LIBRARIES:=
 LOCAL_CLASSPATH:=
 LOCAL_DROIDDOC_USE_STANDARD_DOCLET:=