Cached NTP time for system services.

Uses NTP server and timeout from secure settings, or fallback to
defaults in resources.  Update various system services to use cached
NTP time when fresh enough, or force updates as needed.

Bug: 4517273
Change-Id: Ie1c4c4883836013d02ca0bbd850cf8949f93b34b
diff --git a/core/java/android/provider/Settings.java b/core/java/android/provider/Settings.java
index 65babc2..23b53ae 100644
--- a/core/java/android/provider/Settings.java
+++ b/core/java/android/provider/Settings.java
@@ -3833,6 +3833,11 @@
         /** {@hide} */
         public static final String NETSTATS_TAG_MAX_HISTORY = "netstats_tag_max_history";
 
+        /** Preferred NTP server. {@hide} */
+        public static final String NTP_SERVER = "ntp_server";
+        /** Timeout in milliseconds to wait for NTP server. {@hide} */
+        public static final String NTP_TIMEOUT = "ntp_timeout";
+
         /**
          * @hide
          */