MacViews: Implement Full Keyboard Access.

ui/message_center/views/message_center_view.cc

Index: ui/message_center/views/message_center_view.cc
diff --git a/ui/message_center/views/message_center_view.cc b/ui/message_center/views/message_center_view.cc
index 201c636692c7136bf230a0003cc2210087f69749..e40718629e8b2044b3ceef155c13ea5e7b04cb97 100644
--- a/ui/message_center/views/message_center_view.cc
+++ b/ui/message_center/views/message_center_view.cc
@@ -601,8 +601,16 @@ void MessageCenterView::NotificationsChanged() {
     }
   }
   button_bar_->SetCloseAllButtonEnabled(!no_closable_views);
-  scroller_->SetFocusBehavior(no_message_views ? FocusBehavior::NEVER
-                                               : FocusBehavior::ALWAYS);
+
+  if (no_message_views) {
+    scroller_->SetFocusBehavior(FocusBehavior::NEVER);
+  } else {
+#if defined(OS_MACOSX)
+    scroller_->SetFocusBehavior(FocusBehavior::ACCESSIBLE_ONLY);
+#else
+    scroller_->SetFocusBehavior(FocusBehavior::ALWAYS);
+#endif
+  }
 
   if (focus_manager && focused_view)
     focus_manager->SetFocusedView(focused_view);