Add system trust agents on first boot or when adding user

While we're in there also call listeners when they're added
so they know the state immediately.

Bug: 17258031
Change-Id: I5f1186314795f3fafd78e1b3e2d5102cdaec65d6
diff --git a/core/java/android/provider/Settings.java b/core/java/android/provider/Settings.java
index f4c2dc8..01fda47 100644
--- a/core/java/android/provider/Settings.java
+++ b/core/java/android/provider/Settings.java
@@ -3739,6 +3739,13 @@
                 "show_note_about_notification_hiding";
 
         /**
+         * Set to 1 by the system after trust agents have been initialized.
+         * @hide
+         */
+        public static final String TRUST_AGENTS_INITIALIZED =
+                "trust_agents_initialized";
+
+        /**
          * The Logging ID (a unique 64-bit value) as a hex string.
          * Used as a pseudonymous identifier for logging.
          * @deprecated This identifier is poorly initialized and has