Implement android_app_set module.

Bug: 152319766
Test: manual and builtin
Change-Id: I66edc5b423898a11dbba1c3d9796c7bd4d6b4428
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 5af0570..c88a1cd 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -21,6 +21,7 @@
 LOCAL_APIDIFF_NEWAPI:=
 LOCAL_APIDIFF_OLDAPI:=
 LOCAL_APK_LIBRARIES:=
+LOCAL_APK_SET_MASTER_FILE:=
 LOCAL_ARM_MODE:=
 LOCAL_ASFLAGS:=
 LOCAL_ASSET_DIR:=