Gtk3: Fix black patches on GtkFileChooser dialogs

chrome/browser/ui/libgtkui/gtk_util.h

Index: chrome/browser/ui/libgtkui/gtk_util.h
diff --git a/chrome/browser/ui/libgtkui/gtk_util.h b/chrome/browser/ui/libgtkui/gtk_util.h
index 95feec21edce91584df4cc15df4b17aaabd5bf04..ab335cdb0d6857283f2fc0ca8a2d5dcd18a92ec8 100644
--- a/chrome/browser/ui/libgtkui/gtk_util.h
+++ b/chrome/browser/ui/libgtkui/gtk_util.h
@@ -174,6 +174,8 @@ void ApplyCssToContext(GtkStyleContext* context, const std::string& css);
 // GetStyleContextFromCss(|css_selector|).
 SkColor GetFgColor(const std::string& css_selector);
 
+ScopedCssProvider GetCssProvider(const std::string& css);
+
 // Renders the backgrounds of all ancestors of |context|, then renders
 // the background for |context| itself.
 void RenderBackground(const gfx::Size& size,