Ensure default dialog button focus remains after a dialog update.

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 094d098e299b5c7a4d9569c5fbad0d282d2ef40b..db3dc2f5e37ec4cd7739c3c244737ab2d0eda775 100644
--- a/ui/views/window/dialog_client_view.cc
+++ b/ui/views/window/dialog_client_view.cc
@@ -19,6 +19,7 @@
 #include "ui/views/layout/grid_layout.h"
 #include "ui/views/layout/layout_provider.h"
 #include "ui/views/style/platform_style.h"
+#include "ui/views/view_observer.h"
 #include "ui/views/widget/widget.h"
 #include "ui/views/window/dialog_delegate.h"
 
@@ -50,6 +51,36 @@ gfx::Size GetBoundingSizeForVerticalStack(const gfx::Size& size1,
                    size1.height() + size2.height());
 }
 
+// ViewDeletionObserver implements an observer to track the deletion of the
+// view in focus.
+class ViewDeletionObserver : public ViewObserver {
+ public:
+  explicit ViewDeletionObserver(View* observed_view)
+      : observed_view_(observed_view) {
+    if (observed_view_)
+      observed_view_->AddObserver(this);
+  }
+
+  ~ViewDeletionObserver() override {
+    if (observed_view_)
+      observed_view_->RemoveObserver(this);
+  }
+
+  // ViewObserver:
+  void OnViewIsDeleting(View* observed_view) override {
+    DCHECK_EQ(observed_view, observed_view_);
+    observed_view_ = nullptr;
+    observed_view_->RemoveObserver(this);
+  }
+
+  View* observed_view() { return observed_view_; }
+
+ private:
+  View* observed_view_ = nullptr;
+
+  DISALLOW_COPY_AND_ASSIGN(ViewDeletionObserver);
+};
+
 }  // namespace
 
 // Simple container to bubble child view changes up the view hierarchy.
@@ -326,6 +357,8 @@ void DialogClientView::SetupLayout() {
   base::AutoReset<bool> auto_reset(&adding_or_removing_views_, true);
   GridLayout* layout = new GridLayout(button_row_container_);
   layout->set_minimum_size(minimum_size_);
+  FocusManager* focus_manager = GetFocusManager();
+  ViewDeletionObserver deletion_observer(focus_manager->GetFocusedView());
 
   // Clobber any existing LayoutManager since it has weak references to child
   // Views which may be removed by SetupViews().
@@ -413,6 +446,14 @@ void DialogClientView::SetupLayout() {
     column_set->LinkColumnSizes(link[0], link[1], link[2], -1);
 
   layout->AddPaddingRow(kFixed, insets.bottom());
+
+  // The default focus is lost when child views are added back into the dialog.
+  // This restores focus if the button is still available.
+  View* previously_focused_view = deletion_observer.observed_view();
+  if (previously_focused_view && !focus_manager->GetFocusedView() &&
+      Contains(previously_focused_view)) {
+    previously_focused_view->RequestFocus();
+  }
 }
 
 void DialogClientView::SetupViews() {