Merge 123377 - Crash when setting empty class name on a new element

Merge 123377 - Crash when setting empty class name on a new element
https://bugs.webkit.org/show_bug.cgi?id=92024

Reviewed by Andreas Kling.

Source/WebCore: 

Add a check for null attributeData() when setting the className to an
empty string on a newly created element. New SVG elements have null
attributeData() on baseVal upon creation.

Test: svg/custom/empty-className-baseVal-crash.html

* dom/StyledElement.cpp:
(WebCore::StyledElement::classAttributeChanged): Add check for null attributeData()

LayoutTests: 

Add a check for null attributeData() when setting the className to an
empty string on a newly created element.

* svg/custom/empty-className-baseVal-crash-expected.txt: Added.
* svg/custom/empty-className-baseVal-crash.html: Added.


TBR=schenney@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=124076