Use the default theme as the fallback UI in Blink

ui/native_theme/fallback_theme.h

Index: ui/native_theme/fallback_theme.h
diff --git a/ui/native_theme/fallback_theme.h b/ui/native_theme/fallback_theme.h
new file mode 100644
index 0000000000000000000000000000000000000000..65bfc3ac61306cfbca5ebefd62283ac8d8d299c0
--- /dev/null
+++ b/ui/native_theme/fallback_theme.h
@@ -0,0 +1,31 @@
+// Copyright (c) 2012 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_NATIVE_THEME_FALLBACK_THEME_H_
+#define UI_NATIVE_THEME_FALLBACK_THEME_H_
+
+#include "ui/native_theme/native_theme_base.h"
+
+namespace ui {
+
+// This theme can draw UI controls on every platform. We use it when a feature
+// is missing from the native theme.

[sky, 2013/04/26 16:13:50]

Please indicate this is only used when scaling and the native theme doesn't
support the scale.

[keishi, 2013/04/30 08:16:58]

Done.

+class NATIVE_THEME_EXPORT FallbackTheme : public NativeThemeBase {
+ public:
+  static FallbackTheme* instance();
+
+ protected:
+  FallbackTheme();
+  virtual ~FallbackTheme();
+
+ private:
+  // Overridden from NativeThemeBase:
+  virtual SkColor GetSystemColor(ColorId color_id) const OVERRIDE;
+
+  DISALLOW_COPY_AND_ASSIGN(FallbackTheme);
+};
+
+}  // namespace ui
+
+#endif  // UI_NATIVE_THEME_FALLBACK_THEME_H_