Revert "Make the DOM hash ignore text node splitting"

Turns out to be very broken, causes out-of-order character
insertion while typing.

This reverts commit 32b7f47f1cc1c9bf0c021573c6a32a16d40b2ac1.

Change-Id: I71c6d8f380dea4c6b208bc97d5caeac73d377a54