Get RootEditableElement from SelectionForUndoStep

Currently RootEditableElement is calculated by
doing EndingVisibleSelection, which do a layout and canonicalization
which is not required.
So we can use SelectionForUndoStep stored value to
get the RootEditableElement


Change-Id: I3221979236058dd6107154bdbaaf0c5f21cab7af
Commit-Queue: Tanvir Rizvi <>
Reviewed-by: Xiaocheng Hu <>
Reviewed-by: Yoshifumi Inoue <>
Cr-Commit-Position: refs/heads/master@{#495917}
5 files changed