When "transpose" command is canceled by "beforeinput" event handler,
Blink change selection at L1413.

Note: This issue is found by looking  issue 704036 

void Editor::transpose() {
 ....

1410  // Select the two characters.
1411  if (createVisibleSelection(newSelection) !=
1412      frame().selection().computeVisibleSelectionInDOMTreeDeprecated())
1413    frame().selection().setSelection(newSelection);
1414
1415  if (dispatchBeforeInputInsertText(
1416          eventTargetNodeForDocument(frame().document()), transposed,
1417          InputEvent::InputType::InsertTranspose) !=
1418      DispatchEventResult::NotCanceled)
1419    return;