MacViews: Provide CreateNativeWidget and a stub NativeThemeMac in NativeWidgetMac

ui/native_theme/native_theme_mac.h

Index: ui/native_theme/native_theme_mac.h
diff --git a/ui/native_theme/native_theme_mac.h b/ui/native_theme/native_theme_mac.h
index 20378426db5bdac63a7d7a552e15310c852d1f77..d65825cbcbf44561ac539d517e03378a823abf3f 100644
--- a/ui/native_theme/native_theme_mac.h
+++ b/ui/native_theme/native_theme_mac.h
@@ -5,12 +5,14 @@
 #ifndef UI_NATIVE_THEME_NATIVE_THEME_MAC_H_
 #define UI_NATIVE_THEME_NATIVE_THEME_MAC_H_
 
-#include "ui/native_theme/native_theme_base.h"
+#include "ui/native_theme/fallback_theme.h"
+#include "ui/native_theme/native_theme_export.h"
 
 namespace ui {
 
 // Mac implementation of native theme support.
-class NativeThemeMac : public NativeThemeBase {
+// TODO(tapted): This should not use FallbackTheme. http://crbug.com/379086.
+class NativeThemeMac : public FallbackTheme {
  public:
   static NativeThemeMac* instance();