Microdata: names.item() must return null for out of range indexes.
https://bugs.webkit.org/show_bug.cgi?id=97898

Reviewed by Kentaro Hara.

Source/WebCore: 

DOMStringList.item() must return null for an invalid index.
Spec: http://www.w3.org/TR/DOM-Level-3-Core/core.html#DOMStringList
Removed [IsIndex] extended IDL attribute from item() method's index
parameter in DOMStringList interface.
Firefox and Opera's behavior is consistent with the spec. Both
returns null for invalid index.

Test: fast/dom/MicroData/names-item-out-of-range-index.html

* dom/DOMStringList.idl:

LayoutTests: 

Added test case to ensure names.item() behavior for out of range indexes.

* fast/dom/MicroData/names-item-out-of-range-index-expected.txt: Added.
* fast/dom/MicroData/names-item-out-of-range-index.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk/LayoutTests@130026 268f45cc-cd09-0410-ab3c-d52691b4dbfc