Make SelectionEditor::setWithoutValidation() not to use obsoleted layout objects
Before this patch, |SelectionEditor::setWithoutValidation()| calls
|adjustVisibleSelectionInComposedTree()| to update composed tree version of
selection from DOM position. In |adjustVisibleSelectionInComposedTree()|, it
uses layout object in |mostBackwaredCaretPosition()| without updating layout
tree, via |VisibleSelection::computeSelectionType()|.
When |SelectionEditor::setWithoutValidation()| is called during DOM mutation,
e.g. |nodeWillBeRemove()|, Blink uses obsoleted layout object and it is not
This patch fixes above situation to make
|SelectionEditor::setWithoutValidation()| to call
TEST=n/a; it is hard to write a test case, since obsoleted layout object is
still alive and there is no way to know obsoleted layout object.