AX: Need to get line thickness from fraction on web
https://bugs.webkit.org/show_bug.cgi?id=113720

Reviewed by David Kilzer.

Expose the line thickness property for fractions, which is needed to
help determine the type of equation.

Test: platform/mac/accessibility/mathml-line-fraction.html

* accessibility/AccessibilityObject.h:
(WebCore::AccessibilityObject::mathLineThickness):
* accessibility/AccessibilityRenderObject.cpp:
(WebCore::AccessibilityRenderObject::mathLineThickness):
(WebCore):
* accessibility/AccessibilityRenderObject.h:
(AccessibilityRenderObject):
* accessibility/ios/WebAccessibilityObjectWrapperIOS.mm:
(-[WebAccessibilityObjectWrapper accessibilityMathLineThickness]):
* accessibility/mac/WebAccessibilityObjectWrapperMac.mm:
(-[WebAccessibilityObjectWrapper additionalAccessibilityAttributeNames]):
(-[WebAccessibilityObjectWrapper accessibilityAttributeValue:]):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147439 268f45cc-cd09-0410-ab3c-d52691b4dbfc