Front-end admin toolbar dropdowns inaccessible on Chrome/Android

[johnbillion]

The dropdown menus that appear on the first touch of admin toolbar menus with sub-items are inaccessible because the top level menu URL is triggered.

Steps to reproduce:

1. Visit the front-end of your website using Chrome on Android.
2. Click an admin toolbar menu item that has sub-items, eg. the Add New menu, the site name menu or your user profile menu.
3. The sub-menu is triggered, but the browser also immediately navigates to the URL of the top level menu item.

The issue doesn't occur when using these menus in the admin area.

Tested using Chrome 18 on Android 4.2. Theme is TwentyTwelve.

[johnbillion]

Previously: #20614

[kraftner]

Duplicate of #24767.

[SergeyBiryukov]

#24767 is about Twenty Twelve, not toolbar. It may be a similar issue, but should be fixed separately.

[johnbillion]

Duplicate of #25972.