Docserver: Make ParseDocument section-aware, by grouping document structure
by <section> tags.

BUG=236646
R=yoz@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/82793005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237221 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237221