Fix the crash in DesktopBackgroundView::OnPaint

chrome/browser/chromeos/extensions/wallpaper_private_api.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/extensions/wallpaper_private_api.h"
 
 #include <vector>
 
 #include "ash/desktop_background/desktop_background_controller.h"
 #include "ash/shell.h"
@@ skipping 268 matching lines @@
         base::Bind(&WallpaperSetWallpaperFunction::OnFailureOrCancel,
                    this, ""));
     LOG(ERROR) << "Failed to create wallpaper directory.";
     return;
   }
   std::string file_name = GURL(url_).ExtractFileName();
   FilePath file_path = wallpaper_dir.Append(file_name);
   if (file_util::PathExists(file_path) ||
       file_util::WriteFile(file_path, image_data_.c_str(),
                            image_data_.size()) != -1 ) {
+    wallpaper_.EnsureRepsForSupportedScaleFactors();
+    scoped_ptr<gfx::ImageSkia> deep_copy(wallpaper_.DeepCopy());
+    // ImageSkia is not RefCountedThreadSafe. Use a deep copied ImageSkia if
+    // post to another thread.

[oshima, 2012/11/12 16:39:28]

I think you don't have to do this IF you make
wallpaper_ thread safe because there is no refcount update
by two threads.

[bshe, 2012/11/12 19:12:48]

I may understand this wrong. But it looks to me that we may addref on UI thread
when call  SetWallpaperFromImageSkia(which calls setCustomWallpaper in
desktop_background_controller)
http://code.google.com/searchframe#OAMlx_jo-ck/src/ash/desktop_background/des...

and addref on FILE thread in ResizeAndSaveWallpaper(through CreateResizedImage)
http://code.google.com/searchframe#OAMlx_jo-ck/src/chrome/browser/chromeos/lo...
?

On 2012/11/12 16:39:28, oshima wrote:

[oshima, 2012/11/13 17:46:42]

I see, you're right.

     BrowserThread::PostTask(
         BrowserThread::UI, FROM_HERE,
         base::Bind(&WallpaperSetWallpaperFunction::SetDecodedWallpaper,
-                   this));
+                   this, base::Passed(&deep_copy)));
     chromeos::UserImage wallpaper(wallpaper_);
 
     // Generates and saves small resolution wallpaper. Uses CENTER_CROPPED to
     // maintain the aspect ratio after resize.
     chromeos::WallpaperManager::Get()->ResizeAndSaveWallpaper(
         wallpaper,
         file_path.InsertBeforeExtension(chromeos::kSmallWallpaperSuffix),
         ash::CENTER_CROPPED,
         ash::kSmallWallpaperMaxWidth,
         ash::kSmallWallpaperMaxHeight);
   } else {
     BrowserThread::PostTask(
         BrowserThread::UI, FROM_HERE,
         base::Bind(&WallpaperSetWallpaperFunction::OnFailureOrCancel,
                    this, ""));
     LOG(ERROR) << "Failed to save downloaded wallpaper.";
   }
 }
 
-void WallpaperSetWallpaperFunction::SetDecodedWallpaper() {
+void WallpaperSetWallpaperFunction::SetDecodedWallpaper(
+    scoped_ptr<gfx::ImageSkia> wallpaper) {
   chromeos::WallpaperManager* wallpaper_manager =
       chromeos::WallpaperManager::Get();
-  wallpaper_manager->SetWallpaperFromImageSkia(wallpaper_, layout_);
+  wallpaper_manager->SetWallpaperFromImageSkia(*wallpaper.get(), layout_);
   bool is_persistent =
       !chromeos::UserManager::Get()->IsCurrentUserEphemeral();
   chromeos::WallpaperInfo info = {
       url_,
       layout_,
       chromeos::User::ONLINE,
       base::Time::Now().LocalMidnight()
   };
   wallpaper_manager->SetUserWallpaperInfo(email_, info, is_persistent);
   SendResponse(true);
@@ skipping 60 matching lines @@
 }
 
 WallpaperRestoreMinimizedWindowsFunction::
     ~WallpaperRestoreMinimizedWindowsFunction() {
 }
 
 bool WallpaperRestoreMinimizedWindowsFunction::RunImpl() {
   WindowStateManager::RestoreWindows();
   return true;
 }