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

chrome/browser/ui/webui/options2/chromeos/wallpaper_thumbnails_source2.cc

+// 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.
+
+#include "chrome/browser/ui/webui/options2/chromeos/wallpaper_thumbnail_source2.h"
+
+#include "ash/desktop_background/desktop_background_resources.h"
+#include "base/memory/singleton.h"
+#include "base/string_number_conversions.h"
+#include "base/string_piece.h"
+#include "base/string_util.h"
+#include "base/stringprintf.h"
+#include "base/threading/thread_restrictions.h"
+#include "chrome/browser/io_thread.h"
+#include "chrome/browser/ui/webui/chrome_url_data_manager.h"
+#include "chrome/common/url_constants.h"
+#include "content/public/browser/browser_thread.h"
+#include "grit/ui_resources.h"
+#include "net/base/mime_util.h"
+#include "ui/base/resource/resource_bundle.h"
+#include "ui/gfx/codec/png_codec.h"
+
+namespace chromeos {
+namespace options2 {
+
+namespace {
+
+const char kDefaultWallpaperPrefix[] = "default_";
+
+bool ParseIndexFromPath(const std::string& path, int* index) {
+  DCHECK(index);
+  if (!StartsWithASCII(path, kDefaultWallpaperPrefix, false))
+    return false;
+  return base::StringToInt(base::StringPiece(path.begin() +
+      strlen(kDefaultWallpaperPrefix), path.end()), index);
+}
+
+int PathToIDR(const std::string& path) {
+  int idr = -1;
+  int index = ash::GetInvalidWallpaperIndex();
+  if (ParseIndexFromPath(path, &index))
+    idr = ash::GetWallpaperInfo(index).thumb_id;
+  return idr;
+}
+
+}  // namespace
+
+std::string GetDefaultWallpaperThumbnailURL(int index) {
+  return StringPrintf("%s%s%d", chrome::kChromeUIWallpaperThumbnailURL,
+                      kDefaultWallpaperPrefix, index);
+}
+
+bool IsDefaultWallpaperURL(const std::string url, int* wallpaper_index) {
+  DCHECK(wallpaper_index);
+  *wallpaper_index = ash::GetInvalidWallpaperIndex();
+  if (!StartsWithASCII(url, chrome::kChromeUIWallpaperThumbnailURL, false))
+      return false;
+  std::string sub_path = url.substr(strlen(

[flackr, 2012/04/19 20:13:07]

I'm fairly certain StringPiece avoids constructing new strings, in which case we
should use it. Make ParseIndexFromPath take a StringPiece :-).

[bshe, 2012/04/19 21:05:25]

It seems the StartsWithASCII function use std:string arguments. So I need to
either somehow convert the StringPiece to string (this way would be no
difference in terms of efficiency) or wrote similar function as StartsWithASCII
but use StringPiece as arguments. Or maybe just leave it this way since
constructing one string is cheap. Which one do you prefer?

[flackr, 2012/04/20 00:16:50]

bool BasicStringPiece::starts_with should work :).

[bshe, 2012/04/20 15:33:00]

As discussed, StartsWithASCII does a case insensitive check, so probably want to
just construct a sub str here.  

On 2012/04/20 00:16:50, flackr wrote:

+      chrome::kChromeUIWallpaperThumbnailURL));
+  return ParseIndexFromPath(sub_path, wallpaper_index);
+}
+
+WallpaperThumbnailSource::WallpaperThumbnailSource()
+    : DataSource(chrome::kChromeUIWallpaperThumbnailHost, NULL) {
+}
+
+WallpaperThumbnailSource::~WallpaperThumbnailSource() {
+}
+
+void WallpaperThumbnailSource::StartDataRequest(const std::string& path,
+                                                bool is_incognito,
+                                                int request_id) {
+  int idr = PathToIDR(path);
+  if (idr != -1) {
+    DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::IO));
+    const ResourceBundle& rb = ResourceBundle::GetSharedInstance();
+    SendResponse(request_id, rb.LoadDataResourceBytes(idr));
+  }
+}
+
+std::string WallpaperThumbnailSource::GetMimeType(const std::string&) const {
+  return "images/png";
+}
+
+}  // namespace options2
+}  // namespace chromeos