Extract colors from wallpaper and dynamically update login screen overlay

components/wallpaper/wallpaper_manager_base.h

Index: components/wallpaper/wallpaper_manager_base.h
diff --git a/components/wallpaper/wallpaper_manager_base.h b/components/wallpaper/wallpaper_manager_base.h
index 88601cc801e5ad5ce87d5e76e460f08e75e5e7b9..6424e2c05667b7f81ed5e5228baf43766b141b03 100644
--- a/components/wallpaper/wallpaper_manager_base.h
+++ b/components/wallpaper/wallpaper_manager_base.h
@@ -194,8 +194,14 @@ class WALLPAPER_EXPORT WallpaperManagerBase {
   class Observer {
    public:
     virtual ~Observer() {}
+    // Notified when the wallpaper animation finishes.
     virtual void OnWallpaperAnimationFinished(const AccountId& account_id) = 0;
+    // Notified when the wallpaper is updated and the color calculation results
+    // change.
+    virtual void OnWallpaperColorsChanged() {}
+    // Notified when the wallpaper is updated.
     virtual void OnUpdateWallpaperForTesting() {}
+    // Notified when the wallpaper pending list is empty.
     virtual void OnPendingListEmptyForTesting() {}
   };