Excessive DOM Size

[rwestlund]

Lighthouse recommends keeping a web app under total 1500 nodes:
https://developers.google.com/web/tools/lighthouse/audits/dom-size

A single instance of paper-date-picker (v2.0.0) creates creates 556 DOM nodes, which blows more than a third of the DOM budget!

I have paper-date-picker in a card element that I show a list of. This causes my DOM size to balloon into tens of thousands of nodes, which is unusably slow.

It's so slow to stamp that I wonder whether somewhere under the hood the iterations are causing layout thrashing:
https://developers.google.com/web/fundamentals/performance/rendering/avoid-large-complex-layouts-and-layout-thrashing#avoid_layout_thrashing

Anyhow, it looks like the bulk of it is coming from paper-calendar. It's stamping three months at once, with several levels of dom-repeat. Reducing the number of nodes to stamp a month and/or not stamping invisible months would have a large impact on performance. I think the goal should be to get this under 100 nodes.