<core-style/>'s ShadowRoot doesn't update when its content updates

[geppy]

I have a <core-style/> producer whose content contains Polymer expressions. The content of the <core-style/> producer changes when the value of the Polymer expression changes, but the ShadowRoot of the <core-style/> producer is not updated (so the <core-style/> consumer doesn't get updated). I can confirm that this is what's causing the problem, as if I manually update the ShadowRoot of the <core-style/> producer, then the <core-style/> consumer gets updated.

[jakemac53]

This repo just contains wrappers for the JS elements, so most bugs should be file on the primary JS repo and will then get propagated here during the next update. I added googlearchive/core-style#9 over there so you can track it.