In Safari #selectionBar size is wrong if custom font is used

[bashmish]

Description

In Safari when custom font is used on paper-tabs, the size of #selectionBar is wrong.

Expected outcome

The size of #selectionBar is equal to the tab size.

Actual outcome

The size of #selectionBar is longer than needed (sometimes).

Live Demo

https://github.com/bashmish/bug-safari-paper-tabs-custom-font

Steps to reproduce

Clone https://github.com/bashmish/bug-safari-paper-tabs-custom-font.git repo, run bower install && polymer serve, open http://127.0.0.1:8081 and reload the page until you see the wrongly sized #selectionBar. It may happen rarely. But under some circumstances (like we have in our app), it happens more often, probably because it is deeper in the components tree (I didn't find any other correlation).

Browsers Affected

• Chrome
• Firefox
• Safari 10.1.2
• Safari 9 (maybe)
• Safari 8 (maybe)
• Safari 7 (maybe)
• Edge
• IE 11
• IE 10