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 af0caa6be92b60086508c9893db05a0bed266e65..bc10dbd5e6037b65d3cf6ea8d8cc2c921851ee4a 100644
--- a/ui/views/controls/combobox/combobox.cc
+++ b/ui/views/controls/combobox/combobox.cc
@@ -94,6 +94,7 @@ class TransparentButton : public CustomButton {
  public:
   TransparentButton(ButtonListener* listener)
       : CustomButton(listener) {
+    SetFocusBehavior(views::View::FocusBehavior::NEVER);
     SetAnimationDuration(LabelButton::kHoverAnimationDurationMs);
   }
   ~TransparentButton() override {}
@@ -353,7 +354,11 @@ Combobox::Combobox(ui::ComboboxModel* model)
       arrow_button_(new TransparentButton(this)),
       weak_ptr_factory_(this) {
   ModelChanged();
-  SetFocusable(true);
+#if defined(OS_MACOSX)
+  SetFocusBehavior(FocusBehavior::ACCESSIBLE_ONLY);
+#else
+  SetFocusBehavior(FocusBehavior::ALWAYS);
+#endif
   UpdateBorder();
   // set_background() takes ownership but takes a raw pointer.
   std::unique_ptr<Background> b = PlatformStyle::CreateComboboxBackground();
@@ -381,8 +386,6 @@ 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_);
 }