Cleanup: Normalize usage of ExceptionCode in ContainerNode::checkXxxChild()
https://bugs.webkit.org/show_bug.cgi?id=108766

Reviewed by Kentaro Hara.

This patch refactors checkAddChild and checkReplaceChild to remove the
creation of an extra ExceptionCode that's not necessary for the
desired behavior, and to bring the ExceptionCode usage into line with
the rest of WebKit (this was the only case where ExceptionCode was
assigned inside an 'if' statement's condition).

After this patch, 'ec' will always be assigned a value, even if the
result of 'checkAcceptChild' is 0. This would only change behavior if
'ec' was non-zero coming into the function, and 'checkAcceptChild'
returned 0. Since every callsite is either directly after an explicit
zeroing of 'ec', or after an 'if (ec)' clause, that case should never
appear. This patch, therefore, shouldn't visibly change WebKit's
behavior.

* dom/ContainerNode.cpp:
(WebCore::checkAddChild):
(WebCore::checkReplaceChild):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141746 268f45cc-cd09-0410-ab3c-d52691b4dbfc