Don't allow Checkboxes to participate in equal-sized-buttons in Harmony dialogs.

ui/views/window/dialog_client_view.cc

Index: ui/views/window/dialog_client_view.cc
diff --git a/ui/views/window/dialog_client_view.cc b/ui/views/window/dialog_client_view.cc
index 3cd043e2eb325ade6518cbbba973ce97210df3ad..12db11c2fd7229af3aa2b07e78cadfa74dd23ef6 100644
--- a/ui/views/window/dialog_client_view.cc
+++ b/ui/views/window/dialog_client_view.cc
@@ -392,8 +392,11 @@ void DialogClientView::SetupLayout() {
   }
 
   if (ui::MaterialDesignController::IsSecondaryUiMaterial()) {
-    // Only link the extra view column if it is a button.
-    if (views[0] && !CustomButton::AsCustomButton(views[0]))
+    // Only link the extra view column if its View type matches the buttons. And
+    // if there's only buttons or only the extra view, everything can be linked.
+    View* either_button_view = ok_button_ ? ok_button_ : cancel_button_;
+    if (either_button_view && extra_view_ &&

[msw, 2017/05/02 17:20:10]

nit: curlies for multi-line conditional?

[tapted, 2017/05/03 00:16:59]

Broke out a separate bool - condition got a little too messy.

+        either_button_view->GetClassName() != extra_view_->GetClassName())

[msw, 2017/05/02 17:20:10]

Won't this exclude other cases that we would want to be linked? (eg. ok/cancel
is a MdTextButton/BlueButton, but the extra view is a LabelButton), there are
lots of button subclasses... Maybe just exclude checkbox extra views?

[tapted, 2017/05/03 00:16:59]

Done.

I think, because this is only for Harmony, there should only be MdTextButton
(dialogs should be using MdTextButton::CreateSecondaryUi[Blue]Button which will
always be MdTextButton, possibly with SetProminent(true)). And dialogs shouldn't
mix LabelButtons and MdTextButton.

But it could be limiting in other ways, and I like the idea of just excluding
Checkbox (downside is a teeny bit of coupling between DialogClientView and
Checkbox). There is also RadioButton.. but I think we can assume nobody is going
to put that in the extra view slot.

[msw, 2017/05/03 18:21:01]

Random dialogs might be using LabelButton for the extra view.

       column_set->LinkColumnSizes(link[1], link[2], -1);
     else
       column_set->LinkColumnSizes(link[0], link[1], link[2], -1);