Add GN "resources" target for blink_resources GYP target.

I need this to be able to remove blink_common_resources from Chromium.

BUG=338338
TEST=None
R=brettw@chromium.org,
TBR=abarth@chromium.org

Review URL: https://codereview.chromium.org/424503002

git-svn-id: svn://svn.chromium.org/blink/trunk@179053 bbb929c8-8fbe-4397-9dbb-9b2b20218538