Gtk3: Render a GtkHeaderBar as the background of the tab strip

chrome/browser/ui/libgtkui/native_theme_gtk3.cc

Index: chrome/browser/ui/libgtkui/native_theme_gtk3.cc
diff --git a/chrome/browser/ui/libgtkui/native_theme_gtk3.cc b/chrome/browser/ui/libgtkui/native_theme_gtk3.cc
index 84de8bda62613352f85ba48c93b42de0a3952cfd..f901637b6f07f6485e11ee036d5d0f3f4928f4da 100644
--- a/chrome/browser/ui/libgtkui/native_theme_gtk3.cc
+++ b/chrome/browser/ui/libgtkui/native_theme_gtk3.cc
@@ -21,8 +21,7 @@ namespace {
 
 void PaintWidget(SkCanvas* canvas,
                  const gfx::Rect& rect,
-                 const char* css_selector,
-                 GtkStateFlags state) {
+                 GtkStyleContext* context) {
   SkBitmap bitmap;
   bitmap.allocN32Pixels(rect.width(), rect.height());
   bitmap.eraseColor(0);
@@ -33,9 +32,6 @@ void PaintWidget(SkCanvas* canvas,
       cairo_format_stride_for_width(CAIRO_FORMAT_ARGB32, rect.width()));
   cairo_t* cr = cairo_create(surface);
 
-  auto context = GetStyleContextFromCss(css_selector);
-  gtk_style_context_set_state(context, state);
-
   gtk_render_background(context, cr, 0, 0, rect.width(), rect.height());
   gtk_render_frame(context, cr, 0, 0, rect.width(), rect.height());
   cairo_destroy(cr);
@@ -338,7 +334,7 @@ void NativeThemeGtk3::PaintMenuPopupBackground(
     SkCanvas* canvas,
     const gfx::Size& size,
     const MenuBackgroundExtraParams& menu_background) const {
-  PaintWidget(canvas, gfx::Rect(size), "GtkMenu#menu", GTK_STATE_FLAG_NORMAL);
+  PaintWidget(canvas, gfx::Rect(size), GetStyleContextFromCss("GtkMenu#menu"));
 }
 
 void NativeThemeGtk3::PaintMenuItemBackground(
@@ -346,8 +342,23 @@ void NativeThemeGtk3::PaintMenuItemBackground(
     State state,
     const gfx::Rect& rect,
     const MenuItemExtraParams& menu_item) const {
-  PaintWidget(canvas, rect, "GtkMenu#menu GtkMenuItem#menuitem",
-              StateToStateFlags(state));
+  auto context = GetStyleContextFromCss("GtkMenu#menu GtkMenuItem#menuitem");
+  gtk_style_context_set_state(context, StateToStateFlags(state));
+  PaintWidget(canvas, rect, context);
+}
+
+void NativeThemeGtk3::PaintFrameTopArea(
+    SkCanvas* canvas,
+    State state,
+    const gfx::Rect& rect,
+    const FrameTopAreaExtraParams& frame_top_area) const {
+  auto context = GetStyleContextFromCss("#headerbar.header-bar.titlebar");
+  RemoveBorders(context);
+  gtk_style_context_set_state(context,
+                              frame_top_area.is_active
+                                  ? GTK_STATE_FLAG_NORMAL
+                                  : GTK_STATE_FLAG_BACKDROP);
+  PaintWidget(canvas, rect, context);
 }
 
 }  // namespace libgtkui