Add chrome_public_apk and chrome_public_test_apk targets in GN.

The new targets for mass-upstreaming were only added in Gyp. This brings
parity to GN.
BUG=484934

Review URL: https://codereview.chromium.org/1156363002

Cr-Commit-Position: refs/heads/master@{#332005}
4 files changed