Add a "nano" option to LOCAL_PROTOC_OPTIMIZE_TYPE.

Change-Id: I7429015b3c5f7f38b7be01eb2d4927f7a9999c80
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 000ba9e..81a9493 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -118,7 +118,7 @@
 LOCAL_RENDERSCRIPT_TARGET_API:=
 LOCAL_BUILD_HOST_DEX:=
 LOCAL_DEX_PREOPT:= # '',true,false,nostripping
-LOCAL_PROTOC_OPTIMIZE_TYPE:= # lite(default),micro,full
+LOCAL_PROTOC_OPTIMIZE_TYPE:= # lite(default),micro,nano,full
 LOCAL_PROTOC_FLAGS:=
 LOCAL_NO_CRT:=
 LOCAL_PROPRIETARY_MODULE:=