Remove use of index in wallpaper picker code and some refactor

ash/desktop_background/desktop_background_resources.h

-// 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 ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_RESOURCES_H_
-#define ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_RESOURCES_H_
-
-#include <string>
-
-#include "ash/ash_export.h"
-#include "third_party/skia/include/core/SkColor.h"
-
-namespace ash {
-
-enum WallpaperLayout {
-  CENTER,
-  CENTER_CROPPED,
-  STRETCH,
-  TILE,
-};
-
-enum WallpaperResolution {
-  LARGE,
-  SMALL
-};
-
-// Encapsulates wallpaper infomation needed by desktop background view.
-struct ASH_EXPORT WallpaperViewInfo {
-  int id;
-  WallpaperLayout layout;
-};
-
-struct ASH_EXPORT WallpaperInfo {
-  WallpaperViewInfo large_wallpaper;
-  WallpaperViewInfo small_wallpaper;
-};
-
-const SkColor kLoginWallpaperColor = 0xFEFEFE;
-
-ASH_EXPORT int GetDefaultWallpaperIndex();
-ASH_EXPORT int GetGuestWallpaperIndex();
-ASH_EXPORT int GetInvalidWallpaperIndex();
-ASH_EXPORT WallpaperLayout GetLayoutEnum(const std::string& layout);
-ASH_EXPORT int GetSolidColorIndex();
-ASH_EXPORT int GetWallpaperCount();
-ASH_EXPORT const WallpaperInfo& GetWallpaperInfo(int index);
-ASH_EXPORT const WallpaperViewInfo& GetWallpaperViewInfo(int index,
-    WallpaperResolution resolution);
-
-}  // namespace ash
-
-#endif  // ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_RESOURCES_H_