Perf issues

[blasten]

paper-checkbox is doing work on the attached callback that is causing style recalc.

Please consider doing the work later either by using Polymer.RenderStatus.afterNextRender or when it's required if possible.

This is affecting Chrome History.

[danbeam]

note: we dropped <paper-checkbox> from chrome history, so it doesn't affect us any more (but we only dropped it because of performance).

we ended up implementing a subset of the functionality that works the same way but has less logic and didn't need a label