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..31ec5a75c42d4c99f3b6a4a85e1a548d20333304 100644
--- a/ui/views/widget/widget.h
+++ b/ui/views/widget/widget.h
@@ -554,6 +554,10 @@ class VIEWS_EXPORT Widget : public internal::NativeWidgetDelegate,
   // Returns the ThemeProvider that provides theme resources for this Widget.
   virtual ui::ThemeProvider* GetThemeProvider() const;
 
+  // Sets the ThemeProvider which provides theme resources for this Widget.
+  // Widget does not take ownership.
+  void SetThemeProvider(ui::ThemeProvider* theme_provider);
+
   ui::NativeTheme* GetNativeTheme() {
     return const_cast<ui::NativeTheme*>(
         const_cast<const Widget*>(this)->GetNativeTheme());
@@ -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 provided. 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_;