[Payments] Add combobox support to editors.

chrome/browser/ui/views/payments/payment_request_dialog_view.cc

Index: chrome/browser/ui/views/payments/payment_request_dialog_view.cc
diff --git a/chrome/browser/ui/views/payments/payment_request_dialog_view.cc b/chrome/browser/ui/views/payments/payment_request_dialog_view.cc
index 60b397579f8cd27e5aa089008602534e8992d4bd..a6b28a81d415bdb8e12aa12840c60a7f49c094eb 100644
--- a/chrome/browser/ui/views/payments/payment_request_dialog_view.cc
+++ b/chrome/browser/ui/views/payments/payment_request_dialog_view.cc
@@ -161,6 +161,15 @@ void PaymentRequestDialogView::ViewHierarchyChanged(
     const ViewHierarchyChangedDetails& details) {
   // When a view that is associated with a controller is removed from this
   // view's descendants, dispose of the controller.
+
+  // DO NOT SUBMIT Note to reviewer: When we are here, I believe the View is

[Mathieu, 2017/02/14 21:23:54]

See this comment

+  // still valid and not yet destroyed. Line 176 destroys the controller, which
+  // is problematic when the View does get destroyed (see comment in
+  // credit_card_editor_view_controller.h). Can we get notified *after* a View
+  // has been destroyed? Can WidgetObserver observe the view's widget through
+  // OnWidgetDestroyed, so that |details.child->GetWidget()| could become the
+  // key to |controller_map_|? I'm not familiar with GetWidget() enough to know
+  // whether observing the Widget is equivalent to observing the View.

[sky, 2017/02/14 23:19:24]

Is the only way you get here if the ViewStack removes an item? Would it make
sense to have more direct linkage, meaning viewstack calls a function on this
class and then deletes the view?
Another option is to add a OnViewDestroyed() function to ViewObserver and call
it from ~View.

A Widget may have any number of Views contained in it, and views can be removed
from the widget at anytime, not just for deletion. So, it doesn't make sense to
try to tie the lifetimes together.

   if (!details.is_add &&
       controller_map_.find(details.child) != controller_map_.end()) {
     DCHECK(!details.move_view);