autocomplete: Make ContactProvider rank contacts by affinity

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;
 
 package contacts;
 
 // A contact, roughly based on the GData Contact kind:
 // https://developers.google.com/gdata/docs/2.0/elements#gdContactKind
 // All strings are UTF-8 with Unicode byte order marks stripped out.
 message Contact {
-  // Next ID to use: 15
+  // Next ID to use: 16
 
   // Provider-assigned unique identifier.
   optional string contact_id = 1;
 
   // Last time at which this contact was updated within the upstream provider,
   // as given by base::Time::ToInternalValue().
   optional int64 update_time = 2;
 
   // Has the contact been deleted recently within the upstream provider?
   optional bool deleted = 3 [default = false];
 
+  // Affinity between the user and this contact, in the range [0.0, 1.0].
+  // Unset if the affinity is unknown.
+  optional float affinity = 15;
+
   // Taken from https://developers.google.com/gdata/docs/2.0/elements#gdName.
   optional string full_name = 4;
   optional string given_name = 5;
   optional string additional_name = 6;
   optional string family_name = 7;
   optional string name_prefix = 8;
   optional string name_suffix = 9;
 
   // Raw photo data as supplied by the provider.  This data is untrusted and
   // must be decoded within a sandbox by e.g. ImageDecoder before being used.
@@ skipping 60 matching lines @@
 }
 
 // Singleton message used by ContactDatabase to store update-related metadata.
 message UpdateMetadata {
   // Next ID to use: 2
 
   // Time at which the last successful update was started, as given by
   // base::Time::ToInternalValue().
   optional int64 last_update_start_time = 1;
 }