Gtk3: Fix black patches on GtkFileChooser dialogs

ui/base/glib/scoped_gobject.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_BASE_GLIB_SCOPED_GOBJECT_H_
 #define UI_BASE_GLIB_SCOPED_GOBJECT_H_
 
 // Similar in spirit to a std::unique_ptr.
 template <typename T>
 class ScopedGObject {
@@ skipping 12 matching lines @@
 
   ScopedGObject<T>& operator=(const ScopedGObject<T>& other) = delete;
 
   ScopedGObject<T>& operator=(ScopedGObject<T>&& other) {
     reset();
     obj_ = other.obj_;
     other.obj_ = nullptr;
     return *this;
   }
 
+  T* get() { return obj_; }
+
   operator T*() { return obj_; }
 
   void reset(T* obj = nullptr) {
     Unref();
     obj_ = obj;
     Ref();
   }
 
  private:
   void Ref() {
     // Remove the floating reference from |obj_| if it has one.
     if (obj_ && g_object_is_floating(obj_))
       g_object_ref_sink(obj_);
   }
 
   // This function is necessary so that libgtkui can overload it in
   // the case of T = GtkStyleContext.
   void Unref() {
     if (obj_)
       g_object_unref(obj_);
   }
 
   T* obj_;
 };
 
 #endif  // UI_BASE_GLIB_SCOPED_GOBJECT_H_