[Sync] Introduce SyncedSessionWindow type.

components/sync/protocol/session_specifics.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.
 //
 // Sync protocol datatype extension for sessions.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 52 matching lines @@
   // Identifies the index of the current navigation in navigations. For
   // example, if this is 2 it means the current navigation is navigations[2].
   optional int32 current_navigation_index = 4 [default = -1];
   // True if the tab is pinned.
   optional bool pinned = 5 [default = false];
   // If non-empty, this tab is an app tab and this is the id of the extension.
   optional string extension_app_id = 6;
   // Tabs are navigated, and the navigation data is here.
   repeated TabNavigation navigation = 7;
 
-  // Fields 8 through 11 are deprecated.
   // The favicon for the current url the tab is displaying. Either empty
   // or a valid PNG encoded favicon.
-  optional bytes favicon = 8;
+  optional bytes favicon = 8 [deprecated = true];
   // The type of favicon. For now only normal web favicons are supported.
   enum FaviconType { TYPE_WEB_FAVICON = 1; }
-  optional FaviconType favicon_type = 9;
+  optional FaviconType favicon_type = 9 [deprecated = true];
   // The url of the actual favicon (as opposed to the page using the favicon).
-  optional string favicon_source = 11;
+  optional string favicon_source = 11 [deprecated = true];
   // Ids of the currently assigned variations which should be sent to sync.
-  repeated uint64 variation_id = 12;
+  repeated uint64 variation_id = 12 [deprecated = true];
 }
 
 message TabNavigation {
   // The index in the NavigationController. If this is -1, it means this
   // TabNavigation is bogus.
   // optional int32 index = 1 [default = -1];  // obsolete.
   // The virtual URL, when nonempty, will override the actual URL of the page
   // when we display it to the user.
   optional string virtual_url = 2;
   // The referring URL, which can be empty.
@@ skipping 62 matching lines @@
   }
   // Whether the Password Manager saw a password field on the page.
   optional PasswordState password_state = 26;
 }
 
 // Navigation information for a single redirection within a single navigation.
 message NavigationRedirect {
   // A URL that redirected while navigating to the virtual_url.
   optional string url = 1;
 }