Replace the index mapping of wallpaper picker UI and hard coded wallpaper index in C++

ash/desktop_background/desktop_background_resources.cc

 // 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.
 
 #include "ash/desktop_background/desktop_background_resources.h"
 
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "grit/ui_resources.h"
 #include "ui/base/resource/resource_bundle.h"
@@ skipping 205 matching lines @@
     {
         IDR_AURA_WALLPAPERS_5_GRADIENT7,
         IDR_AURA_WALLPAPERS_5_GRADIENT7_THUMB,
         ash::TILE,
         "Chromium",
         "http://www.chromium.org"
     },
 };
 
 const int kDefaultWallpaperCount = arraysize(kDefaultWallpapers);
+const int kInvalidWallpaperIndex = -1;
 
 // TODO(saintlou): These hardcoded indexes, although checked against the size
 // of the array are really hacky.
 #if defined(GOOGLE_CHROME_BUILD)
 const int kDefaultWallpaperIndex = 16; // IDR_AURA_WALLPAPERS_3_URBAN0
 const int kGuestWallpaperIndex = 26;   // IDR_AURA_WALLPAPERS_5_GRADIENT6
 #else
 const int kDefaultWallpaperIndex = 0;
 const int kGuestWallpaperIndex = kDefaultWallpaperIndex;
 #endif
 
 }  // namespace
 
 namespace ash {
 
+int GetInvalidWallpaperIndex() {
+  return kInvalidWallpaperIndex;
+}
+
 int GetDefaultWallpaperIndex() {
   DCHECK(kDefaultWallpaperIndex < kDefaultWallpaperCount);
   return std::min(kDefaultWallpaperIndex, kDefaultWallpaperCount - 1);
 }
 
 int GetGuestWallpaperIndex() {
   DCHECK(kGuestWallpaperIndex < kDefaultWallpaperCount);
   return std::min(kGuestWallpaperIndex, kDefaultWallpaperCount - 1);
 }
 
 int GetWallpaperCount() {
   return kDefaultWallpaperCount;
 }
 
 const SkBitmap& GetWallpaper(int index) {
   DCHECK(index >= 0 && index < kDefaultWallpaperCount);
   return *ui::ResourceBundle::GetSharedInstance().GetImageNamed(
       kDefaultWallpapers[index].id).ToSkBitmap();
 }
 
-const SkBitmap& GetWallpaperThumbnail(int index) {
-  DCHECK(index >= 0 && index < kDefaultWallpaperCount);
-  return *ui::ResourceBundle::GetSharedInstance().GetImageNamed(
-      kDefaultWallpapers[index].thumb_id).ToSkBitmap();
-}
-
 const WallpaperInfo& GetWallpaperInfo(int index) {
   return kDefaultWallpapers[index];
 }
 
 }  // namespace ash