[Sync] Remove required fields from SyncEntity and obsolete ThrottleParameters.

components/sync/protocol/sync.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 for communication between sync client and server.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 161 matching lines @@
   // will interpret this entity as a newly-created item and generate a
   // new server ID and an initial version number.  If nonzero in a
   // CommitMessage, this item is treated as an update to an existing item, and
   // the server will use |id_string| to locate the item.  Then, if the item's
   // current version on the server does not match |version|, the commit will
   // fail for that item.  The server will not update it, and will return
   // a result code of CONFLICT.  In a GetUpdatesResponse, |version| is
   // always positive and indentifies the revision of the item data being sent
   // to the client.
   // Present in both GetUpdatesResponse and CommitMessage.
-  required int64 version = 4;
+  // WARNING: This field used to be required before M60. Any client before this
+  // will fail to deserialize if this field is missing.
+  optional int64 version = 4;
 
   // Last modification time (in java time milliseconds)
   // Present in both GetUpdatesResponse and CommitMessage.
   optional int64 mtime = 5;
 
   // Creation time.
   // Present in both GetUpdatesResponse and CommitMessage.
   optional int64 ctime = 6;
 
   // The name of this item.
   // Historical note:
   //   Since November 2010, this value is no different from non_unique_name.
   //   Before then, server implementations would maintain a unique-within-parent
   //   value separate from its base, "non-unique" value.  Clients had not
   //   depended on the uniqueness of the property since November 2009; it was
   //   removed from Chromium by http://codereview.chromium.org/371029 .
   // Present in both GetUpdatesResponse and CommitMessage.
-  required string name = 7;
+  // WARNING: This field used to be required before M60. Any client before this
+  // will fail to deserialize if this field is missing.
+  optional string name = 7;
 
   // The name of this item.  Same as |name|.
   // |non_unique_name| should take precedence over the |name| value if both
   // are supplied.  For efficiency, clients and servers should avoid setting
   // this redundant value.
   // Present in both GetUpdatesResponse and CommitMessage.
   optional string non_unique_name = 8;
 
   // A value from a monotonically increasing sequence that indicates when
   // this item was last updated on the server. This is now equivalent
@@ skipping 747 matching lines @@
   required string email = 1;          // the user's full primary email address.
   optional string display_name = 2;   // the user's display name.
   optional string obfuscated_id = 3;  // an obfuscated, opaque user id.
 };
 
 message AuthenticateResponse {
   // Optional only for backward compatibility.
   optional UserIdentification user = 1;
 };
 
-message ThrottleParameters {
-  // Deprecated. Remove this from the server side.
-  required int32 min_measure_payload_size = 1;
-  required double target_utilization = 2;
-  required double measure_interval_max = 3;
-  required double measure_interval_min = 4;
-  required double observation_window = 5;
-};
-
 message ClientToServerResponse {
   optional CommitResponse commit = 1;
   optional GetUpdatesResponse get_updates = 2;
   optional AuthenticateResponse authenticate = 3;
 
   // Up until protocol_version 24, the default was SUCCESS which made it
   // impossible to add new enum values since older clients would parse any
   // out-of-range value as SUCCESS. Starting with 25, unless explicitly set,
   // the error_code will be UNKNOWN so that clients know when they're
   // out-of-date. Note also that when using protocol_version < 25,
@@ skipping 53 matching lines @@
 message EventResponse {};
 
 // A message indicating that the sync engine has been disabled on a client.
 message SyncDisabledEvent {
   // The GUID that identifies the sync client.
   optional string cache_guid = 1;
 
   // The store birthday that the client was using before disabling sync.
   optional string store_birthday = 2;
 };