Make Element::synchronizeAllAttributes() private
Make Element::synchronizeAllAttributes() private

Make Element::synchronizeAllAttributes() private instead of public. Now that
Element::attributes() calls synchronizeAllAttributes() internally, there is
no reason for external code to call it.

R=adamk@chromium.org

Review URL: https://codereview.chromium.org/448063004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@179752 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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