Invalidate all wallpaper cache if display configuration changed

ash/desktop_background/user_wallpaper_delegate.h

Index: ash/desktop_background/user_wallpaper_delegate.h
diff --git a/ash/desktop_background/user_wallpaper_delegate.h b/ash/desktop_background/user_wallpaper_delegate.h
index e1e7f70e52b464e0e0309ad22cfed4380c2dbca0..faeefa47107e095197563c2ac32ff70d082e12a7 100644
--- a/ash/desktop_background/user_wallpaper_delegate.h
+++ b/ash/desktop_background/user_wallpaper_delegate.h
@@ -31,8 +31,11 @@ class ASH_EXPORT UserWallpaperDelegate {
   virtual bool ShouldShowInitialAnimation() = 0;
 
   // Updates current wallpaper. It may switch the size of wallpaper based on the
-  // current display's resolution.
-  virtual void UpdateWallpaper() = 0;
+  // current display's resolution. If |clear_cache| is true, all wallpaper
+  // cache should be cleared. This is required when screen size changes and we
+  // need to load a different resolution wallpaper. All the previous wallpaper

[oshima, 2014/03/13 20:13:39]

we need to clear the cache only if one of displays' pixel size becomes bigger
than one stored in the cache.

Do we really clearing the cache for all display change?

Can you also mentioned about memory vs disk cache? I assume this is in memory
cache and won't clear disk cache right?

[bshe, 2014/03/13 22:16:47]

Sorry. The comment is not misleading. UpdateWallpeper is only called when
displays' pixel size is larger than previous stored value.

On 2014/03/13 20:13:39, oshima wrote:

+  // cache should be cleared.
+  virtual void UpdateWallpaper(bool clear_cache) = 0;
 
   // Initialize wallpaper.
   virtual void InitializeWallpaper() = 0;