Remove use of index in wallpaper picker code and some refactor

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/desktop_background/desktop_background_controller.h"
 #include "ash/shell.h"
 #include "ash/shell/shell_delegate_impl.h"
 #include "ash/shell/window_watcher.h"
@@ skipping 84 matching lines @@
 
   ash::shell::ShellDelegateImpl* delegate = new ash::shell::ShellDelegateImpl;
   ash::Shell::CreateInstance(delegate);
   ash::Shell::GetInstance()->set_browser_context(browser_context_.get());
 
   window_watcher_.reset(new ash::shell::WindowWatcher);
   delegate->SetWatcher(window_watcher_.get());
 
   ash::shell::InitWindowTypeLauncher();
 
-  Shell::GetInstance()->desktop_background_controller()->SetDefaultWallpaper(0);
+  DesktopBackgroundController* controller =
+      Shell::GetInstance()->desktop_background_controller();
+  if (controller->GetAppropriateResolution() == WALLPAPER_RESOLUTION_LARGE)
+    controller->SetDefaultWallpaper(kDefaultLargeWallpaper);
+  else
+    controller->SetDefaultWallpaper(kDefaultSmallWallpaper);
 
   ash::Shell::GetPrimaryRootWindow()->ShowRootWindow();
 }
 
 void ShellBrowserMainParts::PostMainMessageLoopRun() {
   browser_context_.reset();
 
   window_watcher_.reset();
   ash::Shell::DeleteInstance();
   aura::Env::DeleteInstance();
 }
 
 bool ShellBrowserMainParts::MainMessageLoopRun(int* result_code) {
   MessageLoopForUI::current()->Run();
   return true;
 }
 
 }  // namespace shell
 }  // namespace ash