Dropdown displays warnings when clicked

[kreinholt]

Description

When the dropdown is clicked or an item is selected with DevTools open, 3 warnings are displayed stating KeyframeEffect is not defined.

Expected outcome

No warning messages

Actual outcome

3 warning messages

Live Demo

https://www.webcomponents.org/element/PolymerElements/paper-dropdown-menu

Steps to reproduce

1. Goto https://www.webcomponents.org/element/PolymerElements/paper-dropdown-menu
2. Open Dev Tools
3. Click 'brontosaurus'

Browsers Affected

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

[joostdebruijn]

For others with the same issue: updating to neon-animation@2.1.0 causes this warning tobecome an error causing the paper-dropdown-menu element to stop working. To prevent that, pin neon-animation to 2.0.2 in your Bower-file.

[notwaldorf]

cc @e111077