https://bugs.webkit.org/show_bug.cgi?id=77001

Reviewed by Andreas Kling.

Source/WebCore:

This bug was introduced by r105502 but was exposed by r105738.
The image-source of a border-image is not mandatory therefore it
may happen that you have no value set for it. WebCore::createBorderImageValue
was wrongly assuming that the image is always set. This problem also required a bit
of refactoring in CSSStyleSelector::mapNinePieceImage to take into account that
the image could be optional (just like other properties).

Test: fast/css/border-image-null-image-crash.html

* css/CSSBorderImage.cpp:
(WebCore::createBorderImageValue):
* css/CSSStyleSelector.cpp:
(WebCore::CSSStyleSelector::mapNinePieceImage):

LayoutTests:

Add a new test to cover this crash specifically.

* fast/css/border-image-null-image-crash-expected.txt: Added.
* fast/css/border-image-null-image-crash.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@105898 268f45cc-cd09-0410-ab3c-d52691b4dbfc