Integrate protocol buffer compiler into the build system.

Bug: 3152546
Change-Id: Ida3ca3d633ce45704dc8e80d044cdbd3ca69aca5
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index e0c2ed4..775a1b8 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -102,6 +102,7 @@
 LOCAL_RENDERSCRIPT_INCLUDES:=
 LOCAL_BUILD_HOST_DEX:=
 LOCAL_DEX_PREOPT:=
+LOCAL_PROTOC_OPTIMIZE_TYPE:= # lite(default),micro,full
 
 # Trim MAKEFILE_LIST so that $(call my-dir) doesn't need to
 # iterate over thousands of entries every time.