Bug 912904 - [System][Dialogs][ActionMenu] Dialogs & Action menus (BB) a...

...re not scrolling as expected when there is a large list of items. r=alive,kaze

This PR tries to re-land bug 912904. Integration test was failing due to some weird thing related with wallpaper & settings, and with Today's build is working as expected.

Issue related is https://tbpl.mozilla.org/php/getParsedLog.php?id=27715778&tree=B2g-Inbound. You can reproduce with yesterday's build.