Bug 5428541: Check that span is still in text before deleting

This is a cherry-pick in MR0 of CL 141388 from master.

Bug 5488537

In case the span has been removed from the text since the popup
was showed, the delete action is a no-op.

Change-Id: Iec2aeaf03becd82ad44715d5c08bfaa8f62aa3fe