[Sync] Deprecate sync session page state field

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 81 matching lines @@
   // 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.
   optional string referrer = 3;
   // The title of the page.
   optional string title = 4;
   // Content state is an opaque blob created by WebKit that represents the
   // state of the page. This includes form entries and scroll position for each
   // frame.
-  optional string state = 5;
+  // optional string state = 5;  // obsolete.

[maxbogue, 2015/10/23 00:53:28]

Is it customary to comment out deprecated fields like this in Chromium? I've
only ever seen it done by adding [deprecated = true] elsewhere. Or removing the
field entirely if the proto is never stored, which I don't think applies here.

   // The core transition type.
   optional SyncEnums.PageTransition page_transition = 6 [default = TYPED];
   // If this transition was triggered by a redirect, the redirect type.
   optional SyncEnums.PageTransitionRedirectType redirect_type = 7;
   // The unique navigation id (within this client).
   optional int32 unique_id = 8;
   // Timestamp for when this navigation last occurred (in client time).
   // If the user goes back/foward in history the timestamp may refresh.
   optional int64 timestamp_msec = 9;
   // User used the Forward or Back button to navigate among browsing history.
@@ skipping 37 matching lines @@
   // Correct referrer policy. Valid enums are defined in
   // third_party/WebKit/public/platform/WebReferrerPolicy.h.
   optional int32 correct_referrer_policy = 25 [default = 1];
 }
 
 // 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;
 }