Java used-by API list generation

Wrap the dexdeps output content with "<externals></externals>" to
simplify backend xml parsing.

Test: TARGET_BUILD_APPS=com.android.adbd m dist apps_only
Change-Id: I1457eb9558763e50911dc9c689b9bc3fb833a52c
diff --git a/scripts/gen_java_usedby_apex.sh b/scripts/gen_java_usedby_apex.sh
index 251d7aa..0cadb1a 100755
--- a/scripts/gen_java_usedby_apex.sh
+++ b/scripts/gen_java_usedby_apex.sh
@@ -30,9 +30,11 @@
   shift
   rm -f "$out"
   touch "$out"
+  echo "<externals>" >> "$out"
   for x in "$@"; do
     "$dexdeps" "$x" >> "$out" || true
   done
+  echo "</externals>" >> "$out"
 }
 
 if [[ "$1" == "help" ]]