Move SelectionTemplate::is_handle_visible_ to FrameSelection

This patch moves |is_handle_visible_| to |FrameSelection| from |SelectionTemplate|
since handle visibility is used only for setting |FrameSelection|, hence it is
a redundant member variable of |SelectionTemplate|.

Bug: 742093
Change-Id: I3add4da3844fb40be34dcb4d4b46b5fa6fed1d7e
Reviewed-on: https://chromium-review.googlesource.com/595389
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491660}
VisibleSelection Editor::SelectionForCommand(Event* event) {
  VisibleSelection selection =
      GetFrame().Selection().ComputeVisibleSelectionInDOMTree();
  if (!event)
    return selection;
  TextControlElement* text_control_of_selection_start =
      EnclosingTextControl(selection.Start());
  TextControlElement* text_control_of_target =
      IsTextControlElement(*event->target()->ToNode())
          ? ToTextControlElement(event->target()->ToNode())
          : nullptr;
  if (text_control_of_target &&
      (selection.Start().IsNull() ||
       text_control_of_target != text_control_of_selection_start)) {
    const SelectionInDOMTree& select = text_control_of_target->Selection();
    if (!select.IsNone())
      return CreateVisibleSelection(select);
  }
  return selection;
}

VisibleSelection Editor::SelectionForCommand(Event* event) {
  VisibleSelection selection =
      GetFrame().Selection().ComputeVisibleSelectionInDOMTree();
  if (!event)
    return selection;
  TextControlElement* text_control_of_selection_start =
      EnclosingTextControl(selection.Start());
  TextControlElement* text_control_of_target =
      IsTextControlElement(*event->target()->ToNode())
          ? ToTextControlElement(event->target()->ToNode())
          : nullptr;
  if (text_control_of_target &&
      (selection.Start().IsNull() ||
       text_control_of_target != text_control_of_selection_start)) {
    const SelectionInDOMTree& select = text_control_of_target->Selection();
    if (!select.IsNone())
      return CreateVisibleSelection(select);
  }
  return selection;
}
