setAttributeNode() does not set the new value to an existing attribute if specified...

setAttributeNode() does not set the new value to an existing attribute if specified attribute is in a different case.
https://bugs.webkit.org/show_bug.cgi?id=120293

Reviewed by Darin Adler.

Source/WebCore:

setAttributeNode() performs a case-insensitive search for an existing
attribute. If an existing attribute is found, it retrieves the index of
such an attribute. For setting the attribute's new value, we call upon
setAttributeInternal() to which both the index as well as the name of
the attribute is passed.
The name passed to this method is the same as the one passed to the
setAttributeNode() API from the webpage and thus can be in any case.

However, setAttributeInternal() uses this name to get the corresponding
existing attribute node. Since this retrieval is not case-insensitive,
the existing node is not returned and thus the new value is not set on
the existing node.
We should instead use the passed index and use that to retrieve the
existing node.

Note that obtaining the attribute's value using getAttributeNode() would
still return the correct value, i.e. the new one.

Also, this change shall make our behavior similar to that of FF and IE.

Test: fast/dom/Element/setAttributeNode-for-existing-attribute.html

* dom/Element.cpp:
(WebCore::Element::setAttributeInternal):
If the passed index is not equal to attributeNotFound, we use that index
to retrieve the existing attribute.

LayoutTests:

* fast/dom/Element/setAttributeNode-for-existing-attribute-expected.txt: Added.
* fast/dom/Element/setAttributeNode-for-existing-attribute.html: Added.
Layout testcase for verifying that the new attribute value is set properly
if an existing attribute with the same name exists.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@154881 268f45cc-cd09-0410-ab3c-d52691b4dbfc