Add ability for Widgets to override the DefaultThemeProvider

ui/views/widget/widget.h

Index: ui/views/widget/widget.h
diff --git a/ui/views/widget/widget.h b/ui/views/widget/widget.h
index 320332bec2461bd309d694e3651eabc7ba38c712..7b93eec5de25c71df536292627711f4ec865bfb3 100644
--- a/ui/views/widget/widget.h
+++ b/ui/views/widget/widget.h
@@ -266,6 +266,10 @@ class VIEWS_EXPORT Widget : public internal::NativeWidgetDelegate,
     std::string wm_role_name;
     std::string wm_class_name;
     std::string wm_class_class;
+
+    // Specifies a theme_provider to be used in place of
+    // |default_theme_provider_|. Widget does not take ownership.
+    ui::ThemeProvider* theme_provider;
   };
 
   Widget();
@@ -884,6 +888,10 @@ class VIEWS_EXPORT Widget : public internal::NativeWidgetDelegate,
   // A theme provider to use when no other theme provider is specified.
   scoped_ptr<ui::DefaultThemeProvider> default_theme_provider_;
 
+  // The theme provider to use if specified. Otherwise |default_theme_provider_|
+  // is used. This is not owned by Widget.
+  ui::ThemeProvider* theme_provider_;
+
   // Valid for the lifetime of RunShellDrag(), indicates the view the drag
   // started from.
   View* dragged_view_;