Rename getDataFromDom to getDataFromDomSubtree

To match its inverse getDomSubtreeFromData, and to make clear
that the input can be any subtree, not just a full document.

Change-Id: I4853bb6def0059eda43f86f0dcb6dd44309dc35d
Merge "Rename getDataFromDom to getDataFromDomSubtree"