mdMenu: mdButton that becomes an <a> tag will not take focus on hover

[snaumets]

It seems like normally, hovering over an mdButton item in the menu will also give focus to that element, but when the mdButton becomes an <a> tag, it no longer takes that focus, and the <button> above it in the menu keeps focus, which seems like incorrect/unintentional behavior.
A live example can be seen here. In it, when you hover over any of the 'somethingX' items, it also takes the focus, but when you hover over the 'google' item which is actually a link, it will not steal the focus.

In a mdMenu that consists of mdButtons, each mdButton becomes either a <button> or an <a> tag (when given either an href or ng-href for example). However, the <a> tags dont take the focus when the element is hovered on. It seems that only non-disabled buttons can take the focus.

[jelbourn]

cc @rschmukler

[topherfangio]

Closed in 0627d9e.