Reapply r80770 "Switch from xml.dom.minidom to xml.etree".

TBR=dpranke@chromium.org
BUG=
TEST=

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@80785 0039d316-1c4b-4281-b951-d872f2087c98