Remove lots of code related synchronously attaching

Now that we always lazy attach we can remove the hacks and special
cases related to synchronously attaching.

BUG=276689

Review URL: https://chromiumcodereview.appspot.com/23606020

git-svn-id: svn://svn.chromium.org/blink/trunk@157422 bbb929c8-8fbe-4397-9dbb-9b2b20218538