Refactor ViewsDelegate singleton

ui/views/views_delegate.h

Index: ui/views/views_delegate.h
diff --git a/ui/views/views_delegate.h b/ui/views/views_delegate.h
index 39c7f5a54ea7186b1172a2f84bb16a6c72dd5bd3..e2f33b05caa5e032b7575788c8e6b364d7b61e6d 100644
--- a/ui/views/views_delegate.h
+++ b/ui/views/views_delegate.h
@@ -60,8 +60,8 @@ class NativeWidgetDelegate;
 // framework. It is used to obtain various high level application utilities
 // and perform some actions such as window placement saving.
 //
-// The embedding app must set views_delegate to assign its ViewsDelegate
-// implementation.
+// The embedding app must set the ViewsDelegate instance by instantiating an
+// implementation of ViewsDelegate (the constructor will set the instance).
 class VIEWS_EXPORT ViewsDelegate {
  public:
 #if defined(OS_WIN)
@@ -73,9 +73,11 @@ class VIEWS_EXPORT ViewsDelegate {
   };
 #endif
 
-  ViewsDelegate();
   virtual ~ViewsDelegate();
 
+  // Returns the ViewsDelegate instance if there is one, or nullptr otherwise.
+  static ViewsDelegate* GetInstance();
+
   // Saves the position, size and "show" state for the window with the
   // specified name.
   virtual void SaveWindowPlacement(const Widget* widget,
@@ -160,8 +162,8 @@ class VIEWS_EXPORT ViewsDelegate {
   // Returns a blocking pool task runner given a TaskRunnerType.
   virtual scoped_refptr<base::TaskRunner> GetBlockingPoolTaskRunner();
 
-  // The active ViewsDelegate used by the views system.
-  static ViewsDelegate* views_delegate;
+ protected:
+  ViewsDelegate();
 
  private:
   scoped_ptr<ViewsTouchEditingControllerFactory> views_tsc_factory_;