Test that the order of Custom Element upgrades is as spec'd.

The order used to be non-deterministic but was recently fixed by: http://src.chromium.org/viewvc/blink?view=revision&revision=153873 to match the order implied by the spec: https://dvcs.w3.org/hg/webcomponents/raw-file/tip/spec/custom/index.html#dfn-element-upgrade-algorithm

BUG=234509

Review URL: https://chromiumcodereview.appspot.com/18774003

git-svn-id: svn://svn.chromium.org/blink/trunk@154208 bbb929c8-8fbe-4397-9dbb-9b2b20218538