Remaining accessibility issues

[alice]

• Focus style (usual disclaimer) - perhaps we need to motivate the design team by drawing the default focus ring around everything until they figure it out :)
• disabled state should be reflected in aria-disabled state (note that you can "click" it using the screen reader without this state, triggering the "this shouldn't happen" dialog)
• Keyboard events: http://www.w3.org/TR/wai-aria-practices/#button
• aria-label seems to be unnecessary given the text is in descendant content, but maybe better safe than sorry

[morethanreal]

Added aria-disabled attribute, and removed aria-label in favor of text content. It seems to work with the screenreader. Focus state is still blocked on design.

[alice]

I kind of wish I hadn't joked about the default focus ring, because now I really think that's what we should be doing everywhere. It's no good implementing keyboard accessibility if people can't see where the focus is.

[morethanreal]

I actually agree with @alice about the default blue focus ring. The one implemented in 8cc8a41 is non-standard wrt material design and subtle compared to the default. Re-opening to turn on the default everywhere.