The compiler is very picky about the use of the "disabled" property on
HTMLElement, since it is only defined on certain subclasses of that.
This adds a method to create a button with the correct type to satisfy
the compiler.
Issue #2528
Change-Id: I31cacd62a35acc87b245ab362dbab55d791cf34d
Please note that this CL doesn't add the new control
to the default layout, so it won't show up in our
demo page.
Issue #2362
Change-Id: Ibecf6a7174de7d8eca9049f0b46ae179a03b9c01