Revert "Remove ShouldSetAttached flag to lazyAttach"

This reverts commit dfc6e91da01f3573f34d386c1c7db40838db7296.

git-svn-id: svn://svn.chromium.org/blink/trunk@157445 bbb929c8-8fbe-4397-9dbb-9b2b20218538