Tap event sometimes fails to show menu

[JaimeFerBec]

Description

The 'on-tap' event to display the menu sometimes fails to show the menu. It simply launches the start of the paper-ripple effect and then opens nothing.

Expected outcome

The menu opens after tapping the dropdown-trigger element.

Actual outcome

The menu does not open.

Related issue and demo

You can check a more detailed description of the issue here: PolymerElements/paper-icon-button#84

Proposed solution

Until the tap issue gets fixed I would propose using on-click instead of on-tap on the div that contains the dropdown-trigger. Either that or allow component user to choose which event to use (click or tap) via a dropdown-event attribute.