Make ve.ce.Surface.getSelectionRect() tollerate browser bugs

.getClientRects() somestimes returns an empty collection which causes an
exception to be thrown by rangy. This corresponds to
.getBoundingDocumentRect() returning a hash full of zeroes.

Detect this and handle such ranges separately, by inserting dummy DOM
elements at the selection's beginning and end, then using their
position to determine where the actual selection was.

This behavior is seen sometimes in Opera, and in Chrome by using the link tool on text at the beginning of the document.

Bug: 47772
Change-Id: I4bad882d1d6fb83bcdcfd0de3bfc9af52960c2ff
Merge "Make ve.ce.Surface.getSelectionRect() tollerate browser bugs"