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..ab19d69c2157a501aee6bc8b60e7554e61a70aa2 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 to a
+  // larger size and we need to load a larger resolution wallpaper. All the
+  // previous small resolution wallpaper cache should be cleared.

[oshima, 2014/03/13 22:23:40]

I think the comment is still not clear because screen size changes when you
change the UI scaling or rotate. Can you explicitly say the display's native
resolution (or pixel resolution) has changed?

[bshe, 2014/03/13 23:19:04]

Used native resolution to be more specific.

On 2014/03/13 22:23:40, oshima wrote:

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