Reland "Implement random wallpaper feature"

ash/desktop_background/desktop_background_resources.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/desktop_background/desktop_background_resources.h"
 
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "grit/ui_resources.h"
 #include "ui/base/resource/resource_bundle.h"
@@ skipping 211 matching lines @@
     },
 };
 
 const int kDefaultWallpaperCount = arraysize(kDefaultWallpapers);
 const int kInvalidWallpaperIndex = -1;
 
 // TODO(saintlou): These hardcoded indexes, although checked against the size
 // of the array are really hacky.
 #if defined(GOOGLE_CHROME_BUILD)
 const int kDefaultWallpaperIndex = 16; // IDR_AURA_WALLPAPERS_3_URBAN0
+const int kLastRandomWallpaperIndex = 19; // The first 20 are random.
 const int kGuestWallpaperIndex = 26;   // IDR_AURA_WALLPAPERS_5_GRADIENT6
 #else
 // Set default wallpaper to the grey background for faster wallpaper loading
 // time in browser tests. Otherwise, some of the tests will finish before
 // wallpaper loaded and cause crashes.
 const int kDefaultWallpaperIndex = 6;  // IDR_AURA_WALLPAPERS_5_GRADIENT5
+const int kLastRandomWallpaperIndex = 8;
 const int kGuestWallpaperIndex = kDefaultWallpaperIndex;
 #endif
 
 }  // namespace
 
 namespace ash {
 
 int GetInvalidWallpaperIndex() {
   return kInvalidWallpaperIndex;
 }
 
 int GetDefaultWallpaperIndex() {
   DCHECK(kDefaultWallpaperIndex < kDefaultWallpaperCount);
   return std::min(kDefaultWallpaperIndex, kDefaultWallpaperCount - 1);
 }
 
 int GetGuestWallpaperIndex() {
   DCHECK(kGuestWallpaperIndex < kDefaultWallpaperCount);
   return std::min(kGuestWallpaperIndex, kDefaultWallpaperCount - 1);
 }
 
+int GetRandomWallpaperIndex() {
+  DCHECK(kLastRandomWallpaperIndex < kDefaultWallpaperCount);
+  return base::RandInt(0,
+      std::min(kLastRandomWallpaperIndex, kDefaultWallpaperCount - 1));
+}
+
 int GetWallpaperCount() {
   return kDefaultWallpaperCount;
 }
 
 const WallpaperInfo& GetWallpaperInfo(int index) {
   DCHECK(index >= 0 && index < kDefaultWallpaperCount);
   return kDefaultWallpapers[index];
 }
 
 }  // namespace ash