Pass the ImageSkia by pointer instead of by reference, which will create shallow copy.

chrome/browser/chromeos/login/wallpaper_manager.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 "chrome/browser/chromeos/login/wallpaper_manager.h"
 
 #include <vector>
 
 #include "ash/desktop_background/desktop_background_controller.h"
 #include "ash/desktop_background/desktop_background_resources.h"
@@ skipping 719 matching lines @@
           base::Bind(&WallpaperManager::GetCustomWallpaperInternal,
                      base::Unretained(this), email, info, resolution,
                      false /* do not update wallpaper */));
       return;
     }
     LoadWallpaper(email, info, false /* do not update wallpaper */);
   }
 }
 
 void WallpaperManager::CacheThumbnail(const std::string& email,
-                                      const gfx::ImageSkia& wallpaper) {
+                                      scoped_ptr<gfx::ImageSkia> wallpaper) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
-  custom_wallpaper_thumbnail_cache_[email] = GetWallpaperThumbnail(wallpaper);
+  custom_wallpaper_thumbnail_cache_[email] =
+      GetWallpaperThumbnail(*wallpaper.get());
 }
 
 void WallpaperManager::DeleteWallpaperInList(
     const std::vector<FilePath>& file_list) {
   for (std::vector<FilePath>::const_iterator it = file_list.begin();
        it != file_list.end(); ++it) {
     FilePath path = *it;
     if (!file_util::Delete(path, false)) {
       LOG(ERROR) << "Failed to remove user wallpaper.";
     }
@@ skipping 323 matching lines @@
 
     if (update_wallpaper) {
       ash::Shell::GetInstance()->desktop_background_controller()->
           SetDefaultWallpaper(ash::GetDefaultWallpaperIndex());
     } else {
       ash::Shell::GetInstance()->desktop_background_controller()->
           CacheDefaultWallpaper(ash::GetDefaultWallpaperIndex());
     }
     return;
   }
+  // Generate all reps before passing to another thread.
+  wallpaper.image().EnsureRepsForSupportedScaleFactors();
+  scoped_ptr<gfx::ImageSkia> deep_copy(wallpaper.image().DeepCopy());
 
   BrowserThread::PostTask(
       BrowserThread::FILE,
       FROM_HERE,
       base::Bind(&WallpaperManager::CacheThumbnail,
                  base::Unretained(this), email,
-                 wallpaper.image().DeepCopy()));
+                 base::Passed(&deep_copy)));
   // Only cache user wallpaper at login screen.
   if (!UserManager::Get()->IsUserLoggedIn()) {
     wallpaper_cache_.insert(std::make_pair(email, wallpaper.image()));
   }
   if (update_wallpaper) {
     ash::Shell::GetInstance()->desktop_background_controller()->
         SetCustomWallpaper(wallpaper.image(), layout);
   }
 }
 
@@ skipping 93 matching lines @@
                           FROM_HERE,
                           base::Bind(&WallpaperManager::StartLoad,
                                      base::Unretained(this),
                                      email,
                                      info,
                                      update_wallpaper,
                                      valid_path));
 }
 
 }  // chromeos