ash: Avoid reloading already-resized custom wallpaper.

ash/test/test_user_wallpaper_delegate.cc

 // Copyright 2013 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/test/test_user_wallpaper_delegate.h"
 
+#include "ash/desktop_background/desktop_background_controller.h"
+#include "ash/shell.h"
+
 namespace ash {
 namespace test {
 
+TestUserWallpaperDelegate::TestUserWallpaperDelegate()
+    : update_wallpaper_count_(0) {}
+
+TestUserWallpaperDelegate::~TestUserWallpaperDelegate() {}
+
 void TestUserWallpaperDelegate::UpdateWallpaper() {
   DefaultUserWallpaperDelegate::UpdateWallpaper();
+  if (!custom_wallpaper_.isNull()) {
+    Shell::GetInstance()->desktop_background_controller()->SetCustomWallpaper(
+        custom_wallpaper_, WALLPAPER_LAYOUT_STRETCH);
+  }
   update_wallpaper_count_ ++;
 }
 
 int TestUserWallpaperDelegate::GetUpdateWallpaperCountAndReset() {
   int count = update_wallpaper_count_;
   update_wallpaper_count_ = 0;
   return count;
 }
 
 }  // namespace test
 }  // namespace ash