Reinstate CDATASection (it's back in the spec)

The use counter for createCDATASection was useful:
https://www.w3.org/Bugs/Public/show_bug.cgi?id=27386

Now CDATASection is back in the spec:
https://github.com/whatwg/dom/pull

BUG=437205
R=tkent@chromium.org

Review-Url: https://codereview.chromium.org/2249083002
Cr-Commit-Position: refs/heads/master@{#412377}
5 files changed