Poor performance of many dropdowns on the same page

[adolgoff]

Description

More than 100 dropdowns on the same page take few seconds to render and make page slow to response

Expected outcome

100-200 dropdowns on the same page should not significantly affect the page performance

Actual outcome

On the laptop the page with more than 100 dropdowns in real-life app takes few seconds to render and becomes laggy after the render completed.

Live Demo

https://polymer-repeater-test.herokuapp.com/view2 (Compare to react: https://react-repeater-test.herokuapp.com/menus)

Steps to reproduce

1. Put more than 100 paper-dropdown-menus on the same page
2. Check out the page render performance.

Browsers Affected

• [x] Chrome
• [ ] Firefox
• [ ] Safari 9
• [ ] Safari 8
• [ ] Safari 7
• [ ] Edge
• [ ] IE 11
• [ ] IE 10