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

chrome/browser/ui/webui/options2/chromeos/wallpaper_thumbnail_source2.h

+// Copyright (c) 2011 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 CHROME_BROWSER_UI_WEBUI_OPTIONS2_CHROMEOS_WALLPAPER_THUMBNAIL_SOURCE2_H_
+#define CHROME_BROWSER_UI_WEBUI_OPTIONS2_CHROMEOS_WALLPAPER_THUMBNAIL_SOURCE2_H_
+#pragma once
+
+#include <string>
+
+#include "base/compiler_specific.h"
+#include "chrome/browser/ui/webui/chrome_url_data_manager.h"
+
+namespace chromeos {
+namespace options2 {
+
+// Returns a string consisting of the prefix specified and the index of the
+// image. For example: chrome://wallpaper/default_2.
+std::string GetDefaultWallpaperThumbnailURL(int index);
+
+// Checks if the given URL points to one of the default wallpapers. If it is,
+// returns true and sets |wallpaper_index| to the corresponding index parsed
+// from |url|. For example: chrome://wallpaper/default_2 will set
+// |wallpaper_index| to 2. If not a default wallpaper url, returns false.
+// |url| and |wallpaper_index| must not be NULL.
+bool IsDefaultWallpaperURL(const std::string url, int* wallpaper_index);
+
+// A DataSource for chrome://wallpaper/ URLs.
+class WallpaperThumbnailSource : public ChromeURLDataManager::DataSource {
+ public:
+  WallpaperThumbnailSource();
+
+  // ChromeURLDataManager::DataSource implementation.
+  virtual void StartDataRequest(const std::string& path,
+                                bool is_incognito,
+                                int request_id) OVERRIDE;
+  virtual std::string GetMimeType(const std::string&) const OVERRIDE;
+
+ private:
+  virtual ~WallpaperThumbnailSource();
+
+  DISALLOW_COPY_AND_ASSIGN(WallpaperThumbnailSource);
+};
+
+}  // namespace options2
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_UI_WEBUI_OPTIONS2_CHROMEOS_WALLPAPER_THUMBNAIL_SOURCE2_H_