Gtk3: Fix black patches on GtkFileChooser dialogs

chrome/browser/ui/libgtkui/native_theme_gtk3.h

Index: chrome/browser/ui/libgtkui/native_theme_gtk3.h
diff --git a/chrome/browser/ui/libgtkui/native_theme_gtk3.h b/chrome/browser/ui/libgtkui/native_theme_gtk3.h
index 5317336e9350a1049d1d673eb39775c278b2328d..7d6c3cefe0708d129d3197605dd150814afa9dac 100644
--- a/chrome/browser/ui/libgtkui/native_theme_gtk3.h
+++ b/chrome/browser/ui/libgtkui/native_theme_gtk3.h
@@ -7,18 +7,23 @@
 
 #include "base/macros.h"
 #include "base/optional.h"
+#include "ui/base/glib/glib_signal.h"
+#include "ui/base/glib/scoped_gobject.h"
 #include "ui/native_theme/native_theme_base.h"
 
+typedef struct _GtkCssProvider GtkCssProvider;
+typedef struct _GtkParamSpec GtkParamSpec;
+typedef struct _GtkSettings GtkSettings;
+
 namespace libgtkui {
 
+using ScopedCssProvider = ScopedGObject<GtkCssProvider>;
+
 // A version of NativeTheme that uses GTK3-rendered widgets.
 class NativeThemeGtk3 : public ui::NativeThemeBase {
  public:
   static NativeThemeGtk3* instance();
 
-  // Called when gtk theme changes.
-  void ResetColorCache();
-
   // Overridden from ui::NativeThemeBase:
   SkColor GetSystemColor(ColorId color_id) const override;
   void PaintArrowButton(cc::PaintCanvas* canvas,
@@ -63,8 +68,18 @@ class NativeThemeGtk3 : public ui::NativeThemeBase {
   NativeThemeGtk3();
   ~NativeThemeGtk3() override;
 
+  void SetThemeCssOverride(ScopedCssProvider provider);
+
+  CHROMEG_CALLBACK_1(NativeThemeGtk3,
+                     void,
+                     OnThemeChanged,
+                     GtkSettings*,
+                     GtkParamSpec*);
+
   mutable base::Optional<SkColor> color_cache_[kColorId_NumColors];
 
+  ScopedCssProvider theme_css_override_;
+
   DISALLOW_COPY_AND_ASSIGN(NativeThemeGtk3);
 };