Clean up createDOM() utility function in shadow-dom.js
Clean up createDOM() utility function in shadow-dom.js

BUG=None
R=dglazkov@chromium.org

Review URL: https://codereview.chromium.org/14791010

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@150078 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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