Cache the scaled avatar drawables in the keyguard user switcher

Loading the avatar icons and drawing them into the sized bitmap
turns out to be quite expensive and the cost increases with number
of users. Caching them shaves off several hundred milliseconds from
Keyguard inflation time during user switching on the lockscreen.

For instance, 15ms vs. 750ms with 3 avatars on a certain 7" tablet.

Bug: 7986933
Change-Id: I3e2065bfa25aa263133ba204ca364c3b04d7c0ff
diff --git a/core/java/android/content/Intent.java b/core/java/android/content/Intent.java
index bfc7bf5..65f904f 100644
--- a/core/java/android/content/Intent.java
+++ b/core/java/android/content/Intent.java
@@ -2567,8 +2567,7 @@
     /**
      * Broadcast sent to the system when a user's information changes. Carries an extra
      * {@link #EXTRA_USER_HANDLE} to indicate which user's information changed.
-     * This is only sent to registered receivers, not manifest receivers. It is sent to the user
-     * whose information has changed.
+     * This is only sent to registered receivers, not manifest receivers. It is sent to all users.
      * @hide
      */
     public static final String ACTION_USER_INFO_CHANGED =