Stop looking up custom filter program during style application.

Since StyleResourceLoader::loadPendingShaders will reconcile a newly-created
program vs. cached program anyway, there is no need for us to look up the
program when applying CSS properties.

BUG=259085

Review URL: https://chromiumcodereview.appspot.com/20598006

git-svn-id: svn://svn.chromium.org/blink/trunk@155361 bbb929c8-8fbe-4397-9dbb-9b2b20218538