MacViews: Implement Full Keyboard Access.

ui/views/controls/combobox/combobox.cc

Index: ui/views/controls/combobox/combobox.cc
diff --git a/ui/views/controls/combobox/combobox.cc b/ui/views/controls/combobox/combobox.cc
index 270bdd5e0c701eb0200df5929baf314a3158296a..bba585922d52c8f1d75efa08faac78875e31f129 100644
--- a/ui/views/controls/combobox/combobox.cc
+++ b/ui/views/controls/combobox/combobox.cc
@@ -92,6 +92,7 @@ class TransparentButton : public CustomButton {
  public:
   TransparentButton(ButtonListener* listener)
       : CustomButton(listener) {
+    SetFocusBehavior(FocusBehavior::NEVER);
     SetAnimationDuration(LabelButton::kHoverAnimationDurationMs);
   }
   ~TransparentButton() override {}
@@ -351,7 +352,7 @@ Combobox::Combobox(ui::ComboboxModel* model)
       arrow_button_(new TransparentButton(this)),
       weak_ptr_factory_(this) {
   ModelChanged();
-  SetFocusable(true);
+  SetFocusBehavior(FocusBehavior::CONTROL);
   UpdateBorder();
 
   // Initialize the button images.
@@ -376,8 +377,6 @@ Combobox::Combobox(ui::ComboboxModel* model)
 
   text_button_->SetVisible(true);
   arrow_button_->SetVisible(true);
-  text_button_->SetFocusable(false);
-  arrow_button_->SetFocusable(false);
   AddChildView(text_button_);
   AddChildView(arrow_button_);
 }