Make members of Singleton<T> private and only visible to the singleton type.

views/focus/focus_manager.h

Index: views/focus/focus_manager.h
diff --git a/views/focus/focus_manager.h b/views/focus/focus_manager.h
index 28f97b41c3ee49d104ba1a68a9574096fcba5b92..6eee79dfc091ad9148e7e03e1b878456e28ca474 100644
--- a/views/focus/focus_manager.h
+++ b/views/focus/focus_manager.h
@@ -126,6 +126,9 @@ class FocusManager {
  public:
   class WidgetFocusManager {
    public:
+    // Returns the singleton instance.
+    static WidgetFocusManager* GetInstance();
+
     // Adds/removes a WidgetFocusChangeListener |listener| to the set of
     // active listeners.
     void AddFocusChangeListener(WidgetFocusChangeListener* listener);