Revert r207560 and r207566 to reland r207511.

ash/shell/content_client/shell_browser_main_parts.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 "ash/shell/content_client/shell_browser_main_parts.h"
 
 #include "ash/ash_switches.h"
 #include "ash/desktop_background/desktop_background_controller.h"
 #include "ash/shell.h"
 #include "ash/shell/shell_delegate_impl.h"
@@ skipping 114 matching lines @@
   ash::Shell::CreateInstance(delegate_);
   ash::Shell::GetInstance()->set_browser_context(browser_context_.get());
 
   window_watcher_.reset(new ash::shell::WindowWatcher);
   gfx::Screen* screen = Shell::GetInstance()->GetScreen();
   screen->AddObserver(window_watcher_.get());
   delegate_->SetWatcher(window_watcher_.get());
 
   ash::shell::InitWindowTypeLauncher();
 
-  DesktopBackgroundController* controller =
-      Shell::GetInstance()->desktop_background_controller();
-  if (controller->GetAppropriateResolution() == WALLPAPER_RESOLUTION_LARGE)
-    controller->SetDefaultWallpaper(kDefaultLargeWallpaper);
-  else
-    controller->SetDefaultWallpaper(kDefaultSmallWallpaper);
+  Shell::GetInstance()->desktop_background_controller()->SetDefaultWallpaper(
+      false /* is_guest */);
 
   ash::Shell::GetPrimaryRootWindow()->ShowRootWindow();
 }
 
 void ShellBrowserMainParts::PostMainMessageLoopRun() {
   gfx::Screen* screen = Shell::GetInstance()->GetScreen();
   screen->RemoveObserver(window_watcher_.get());
 
   window_watcher_.reset();
   delegate_->SetWatcher(NULL);
@@ skipping 18 matching lines @@
   browser_context_.reset();
 }
 
 bool ShellBrowserMainParts::MainMessageLoopRun(int* result_code) {
   base::MessageLoopForUI::current()->Run();
   return true;
 }
 
 }  // namespace shell
 }  // namespace ash