Hit-a-Hint couldn't find rounded link elements

[sugyan]

hit a hint function cannot draw hints for some link elements, such as "Twitter Bootstrap" style button.
because... is_viewable function checks document.elementFromPoint(rect.left, rect.top), but it found parent element if link element is rounded.

For example,

<div><a style="display:block; border-radius:4px;" href="foo">foo</a></div>

document.elementFromPoint(rect.left, rect.top); returns div element, it is not a element.

ChromeKeyconfig/Keyconfig/js/chrome_keyconfig.js

Lines 581 to 582 in 5002a42

	var _e = document.elementFromPoint(rect.left, rect.top);
	if (_e && (_e === elem || elem.contains(_e))) return rect;