contacts: Don't save deleted contacts to disk.

chrome/browser/chromeos/contacts/contact.proto

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Protocol buffer definitions for the user's contacts.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
@@ skipping 86 matching lines @@
     }
     optional Protocol protocol = 2 [default = OTHER];
     optional AddressType type = 3;
     optional bool primary = 4 [default = false];
   }
   repeated InstantMessagingAddress instant_messaging_addresses = 14;
 }
 
 // Singleton message used by ContactDatabase to store update-related metadata.
 message UpdateMetadata {
-  // Next ID to use: 2
+  // Next ID to use: 3
 
   // Time at which the last successful update was started, as given by
   // base::Time::ToInternalValue().
   optional int64 last_update_start_time = 1;
+
+  // Latest time that we've seen in a contact's |update_time| field.  Note that
+  // the time may have come from a deleted contact that has been discarded.
+  optional int64 last_contact_update_time = 2;
 }