Revert last week's OrderIterator changes

The original change (https://chromiumcodereview.appspot.com/18162016)
has created several regressions and it seems that the approach could
be improved so reverting for now to dig deeper.

TBR=ojan@chromium.org,cbiesinger@chromium.org

Review URL: https://codereview.chromium.org/19661006

git-svn-id: svn://svn.chromium.org/blink/trunk@154693 bbb929c8-8fbe-4397-9dbb-9b2b20218538