MacViews: draw combobox arrow backgrounds

ui/views/style/mac/combobox_background_mac.h

+// Copyright 2016 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_VIEWS_STYLE_MAC_COMBOBOX_BACKGROUND_MAC_H_
+#define UI_VIEWS_STYLE_MAC_COMBOBOX_BACKGROUND_MAC_H_
+
+#include "base/macros.h"
+#include "ui/views/background.h"
+
+namespace gfx {
+class Canvas;
+}
+
+namespace views {
+
+// This class implements the background of comboboxes. Comboboxes look like
+// this:
+//   ---------------------------
+//   | Option Text... | Arrows |
+//   ---------------------------
+// This class colors the background of the arrows section in accordance with our
+// Mac look and feel.
+class ComboboxBackgroundMac : public Background {
+ public:
+  ComboboxBackgroundMac();
+  ~ComboboxBackgroundMac() override;
+
+  // Background:
+  void Paint(gfx::Canvas* canvas, View* view) const override;
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ComboboxBackgroundMac);
+};
+
+}  // namespace views
+
+#endif  // UI_VIEWS_STYLE_MAC_COMBOBOX_BACKGROUND_MAC_H_