Fix GN features configuration to match GYPs.

Looks like this is on for all platforms as of:
https://src.chromium.org/viewvc/blink?view=rev&revision=182920

BUG=none
TEST=OSX builds.

Review URL: https://codereview.chromium.org/675643002

git-svn-id: svn://svn.chromium.org/blink/trunk@184473 bbb929c8-8fbe-4397-9dbb-9b2b20218538