Add a new GetInstance() method for singleton classes, take 2.

gfx/gtk_native_view_id_manager.h

Index: gfx/gtk_native_view_id_manager.h
diff --git a/gfx/gtk_native_view_id_manager.h b/gfx/gtk_native_view_id_manager.h
index 05cf0d779a3bc0c551e7345888d6f6a4817d436e..e97a852817eeb7c0eebe5dd7cd90c91036ba834f 100644
--- a/gfx/gtk_native_view_id_manager.h
+++ b/gfx/gtk_native_view_id_manager.h
@@ -36,11 +36,11 @@ struct _GtkPreserveWindow;
 // pointers and observes the various signals from the widget for when an X
 // window is created, destroyed etc. Thus it provides a thread safe mapping
 // from NativeViewIds to the current XID for that widget.
-//
-// You get a reference to the global instance with:
-//   Singleton<GtkNativeViewManager>()
 class GtkNativeViewManager {
  public:
+  // Returns the singleton instance.
+  static GtkNativeViewManager* GetInstance();
+
   // Must be called from the UI thread:
   //
   // Return a NativeViewId for the given widget and attach to the various