Add use_icu_alternatives_on_android support to net's gn file.

It's already supported by the gyp file.

BUG=362608

Review URL: https://codereview.chromium.org/281593002

git-svn-id: https://src.chromium.org/chrome/trunk/src/url@270541 4ff67af0-8c30-449e-8e8b-ad334ec8d88c