Move Editor::Transpose() out of Editor class

This patch moves |Editor::Transpose()| out of |Editor| class as preparation of
expanding it into |ExecutTranspose()| in "EditorCommand.cpp" to make |Editor|
class simpler for improving code health.

Following patch will expand |Transpose()| into |ExecutTranspose()|.

Bug: 672405
Change-Id: Icde253623f31813d2b4517c4da7d4798bd5fadf6
Reviewed-on: https://chromium-review.googlesource.com/583880
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#489518}
void Editor::ChangeSelectionAfterCommand(
    const SelectionInDOMTree& new_selection,
    FrameSelection::SetSelectionOptions options) {
  if (new_selection.IsNone())
    return;

  bool selection_did_not_change_dom_position =
      new_selection == GetFrame().Selection().GetSelectionInDOMTree();
  GetFrame().Selection().SetSelection(
      SelectionInDOMTree::Builder(new_selection)
          .SetIsHandleVisible(GetFrame().Selection().IsHandleVisible())
          .Build(),
      options);

  if (selection_did_not_change_dom_position) {
    Client().RespondToChangedSelection(
        frame_, GetFrame().Selection().GetSelectionInDOMTree().Type());
  }
}

void Editor::ChangeSelectionAfterCommand(
    const SelectionInDOMTree& new_selection,
    FrameSelection::SetSelectionOptions options) {
  if (new_selection.IsNone())
    return;

  bool selection_did_not_change_dom_position =
      new_selection == GetFrame().Selection().GetSelectionInDOMTree();
  GetFrame().Selection().SetSelection(
      SelectionInDOMTree::Builder(new_selection)
          .SetIsHandleVisible(GetFrame().Selection().IsHandleVisible())
          .Build(),
      options);

  if (selection_did_not_change_dom_position) {
    Client().RespondToChangedSelection(
        frame_, GetFrame().Selection().GetSelectionInDOMTree().Type());
  }
}
