menu does not grow when submenu opened under shadow dom

[n1ywb]

Description

When using paper-menu-button in conjunction with paper-submenu, neither the menu width nor the menu height grows when a submenu is opened under native shadow dom. Under shady dom it works as expected.

I created a minimal element to reproduce the issue including a test case.

I'm not 100% sure this is a paper-menu-button issue but it's my best guess.

https://github.com/ReadingPlus/paper-menu-sizing-bug

Expected outcome

The menu gets bigger when a submenu is opened (example under shady dom)

Actual outcome

Under shadow dom the menu does not get bigger (example under shadow dom)

Live Demo

https://readingplus.github.io/paper-menu-sizing-bug/components/paper-menu-sizing-bug/demo/index.html?dom=shadow

Steps to reproduce

1. git clone https://github.com/ReadingPlus/paper-menu-sizing-bug
2. cd paper-menu-sizing-bug
3. bower install
4. polymer test

Browsers Affected

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

[n1ywb]

Looks like this patch might be related to this issue: DreamworldSolutions/iron-resizable-behavior@b246ff3