arc: Support pinned apps across Arc-enabled and Arc-disabled platforms.

sync/protocol/app_list_specifics.proto

 // Copyright 2013 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.
 //
 // Sync protocol datatype extension for the app list (aka app launcher).
 
 // Update proto_{value,enum}_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 29 matching lines @@
 
   // Id of the parent (folder) item.
   optional string parent_id = 4;
 
   // Marked OBSOLETE because this is unused for the app list.
   // Which page this item will appear on in the app list.
   optional string OBSOLETE_page_ordinal = 5 [deprecated = true];
 
   // Where on a page this item will appear.
   optional string item_ordinal = 6;
+
+  // Where on a shelf this item will appear.
+  optional string item_pin_ordinal = 7;
+
+  // If item is pinned by policy.
+  optional bool item_pin_by_policy = 8;

[stevenjb, 2016/06/10 18:00:41]

item_pinned_by_policy, but I am not sure we need this, see my top level comment.

[khmel, 2016/06/10 22:08:11]

Done

 }