Add update_engine_stable_client

This is a update_engine console client installed to APEXes so that
scripts can invoke on. This client operates on the IUpdateEngineStable
service.

Test: pass
Bug: 160996544

Change-Id: I0672b7bd1ccd87e35ffb99d7a66e63dffaf7df24
diff --git a/Android.bp b/Android.bp
index b8cff0a..1076c52 100644
--- a/Android.bp
+++ b/Android.bp
@@ -729,3 +729,12 @@
         },
     },
 }
+
+// update_engine header library
+cc_library_headers {
+    name: "libupdate_engine_headers",
+    export_include_dirs: ["."],
+    apex_available: [
+        "com.android.gki.*",
+    ],
+}