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

chrome/common/url_constants.h

Index: chrome/common/url_constants.h
diff --git a/chrome/common/url_constants.h b/chrome/common/url_constants.h
index 4ee5682d5e82e15dd01a7016c0a627fa9595a82f..ae54d228317825933b8819554c24f9dd9fe574fe 100644
--- a/chrome/common/url_constants.h
+++ b/chrome/common/url_constants.h
@@ -88,6 +88,7 @@ extern const char kChromeUISlideshowURL[];
 extern const char kChromeUISystemInfoURL[];
 extern const char kChromeUITermsOemURL[];
 extern const char kChromeUIUserImageURL[];
+extern const char kChromeUIWallpaperThumbnailURL[];
 #endif
 
 #if defined(USE_ASH)
@@ -214,6 +215,7 @@ extern const char kChromeUISimUnlockHost[];
 extern const char kChromeUISlideshowHost[];
 extern const char kChromeUISystemInfoHost[];
 extern const char kChromeUIUserImageHost[];
+extern const char kChromeUIWallpaperThumbnailHost[];
 
 extern const char kChromeUIMenu[];
 extern const char kChromeUINetworkMenu[];