sync: remove use of protobuf extensions in protocol to reduce static init overhead.

chrome/browser/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";
 
 option optimize_for = LITE_RUNTIME;
 option retain_unknown_fields = true;
 
 package sync_pb;
 
+import "app_notification_specifics.proto";
+import "app_setting_specifics.proto";
+import "app_specifics.proto";
+import "autofill_specifics.proto";
+import "bookmark_specifics.proto";
+import "extension_setting_specifics.proto";
+import "extension_specifics.proto";
+import "nigori_specifics.proto";
+import "password_specifics.proto";
+import "preference_specifics.proto";
+import "search_engine_specifics.proto";
+import "session_specifics.proto";
+import "theme_specifics.proto";
+import "typed_url_specifics.proto";
 import "encryption.proto";
 import "sync_enums.proto";
 import "client_commands.proto";
 import "client_debug_info.proto";
 
 // Used for inspecting how long we spent performing operations in different
 // backends. All times must be in millis.
 message ProfilingData {
   optional int64 meta_data_write_time = 1;
   optional int64 file_data_write_time = 2;
   optional int64 user_lookup_time = 3;
   optional int64 meta_data_read_time = 4;
   optional int64 file_data_read_time = 5;
   optional int64 total_request_time = 6;
 }
 
 message EntitySpecifics {
   // If a datatype is encrypted, this field will contain the encrypted
   // original EntitySpecifics. The extension for the datatype will continue
   // to exist, but contain only the default values.
   // Note that currently passwords employ their own legacy encryption scheme and
   // do not use this field.
   optional EncryptedData encrypted = 1;
 
   // To add new datatype-specific fields to the protocol, extend
   // EntitySpecifics.  First, pick a non-colliding tag number by
   // picking a revision number of one of your past commits
   // to src.chromium.org.  Then, in a different protocol buffer
-  // definition that includes this, do the following:
+  // definition, define your message type, and add an optional field
+  // to the list below using the unique tag value you selected.
   //
-  //   extend EntitySpecifics {
-  //     MyDatatypeSpecifics my_datatype = 32222;
-  //   }
+  //  optional MyDatatypeSpecifics my_datatype = 32222;
   //
   // where:
   //   - 32222 is the non-colliding tag number you picked earlier.
   //   - MyDatatypeSpecifics is the type (probably a message type defined
   //     in your new .proto file) that you want to associate with each
   //     object of the new datatype.
   //   - my_datatype is the field identifier you'll use to access the
   //     datatype specifics from the code.
   //
   // Server implementations are obligated to preserve the contents of
-  // EntitySpecifics when it contains unrecognized extensions.  In this
+  // EntitySpecifics when it contains unrecognized fields.  In this
   // way, it is possible to add new datatype fields without having
   // to update the server.
-  extensions 30000 to max;
+  //
+  // Note: The tag selection process is based on legacy versions of the
+  // protocol which used protobuf extensions. We have kept the process
+  // consistent as the old values cannot change.  The 5+ digit nature of the
+  // tags also makes them recognizable (individually and collectively) from
+  // noise in logs and debugging contexts, and creating a divergent subset of
+  // tags would only make things a bit more confusing.
+
+  optional AutofillSpecifics autofill = 31729;
+  optional BookmarkSpecifics bookmark = 32904;
+  optional PreferenceSpecifics preference = 37702;
+  optional TypedUrlSpecifics typed_url = 40781;
+  optional ThemeSpecifics theme = 41210;
+  optional AppNotification app_notification = 45184;
+  optional PasswordSpecifics password = 45873;
+  optional NigoriSpecifics nigori = 47745;
+  optional ExtensionSpecifics extension = 48119;
+  optional AppSpecifics app = 48364;
+  optional SessionSpecifics session = 50119;
+  optional AutofillProfileSpecifics autofill_profile = 63951;
+  optional SearchEngineSpecifics search_engine = 88610;
+  optional ExtensionSettingSpecifics extension_setting = 96159;
+  optional AppSettingSpecifics app_setting = 103656;
 }
 
 message SyncEntity {
   // This item's identifier.  In a commit of a new item, this will be a
   // client-generated ID.  If the commit succeeds, the server will generate
   // a globally unique ID and return it to the committing client in the
   // CommitResponse.EntryResponse.  In the context of a GetUpdatesResponse,
   // |id_string| is always the server generated ID.  The original
   // client-generated ID is preserved in the |originator_client_id| field.
   // Present in both GetUpdatesResponse and CommitMessage.
@@ skipping 237 matching lines @@
 
   required GetUpdatesSource source = 1;
 
   // True only if notifications were enabled for this GetUpdateMessage.
   optional bool notifications_enabled = 2;
 };
 
 message DataTypeProgressMarker {
   // An integer identifying the data type whose progress is tracked by this
   // marker.  The legitimate values of this field correspond to the protobuf
-  // field numbers of all EntitySpecifics extensions supported by the server.
+  // field numbers of all EntitySpecifics fields supported by the server.
   // These values are externally declared in per-datatype .proto files.
   optional int32 data_type_id = 1;
 
   // An opaque-to-the-client sequence of bytes that the server may interpret
   // as an indicator of the client's knowledge state.  If this is empty or
   // omitted by the client, it indicates that the client is initiating a
   // a first-time sync of this datatype.  Otherwise, clients must supply a
   // value previously returned by the server in an earlier GetUpdatesResponse.
   // These values are not comparable or generable on the client.
   //
@@ skipping 35 matching lines @@
   // from_timestamp has been deprecated; clients should use
   // |from_progress_marker| instead, which allows more flexibility.
   optional int64 from_timestamp = 1;
 
   // Indicates the reason for the GetUpdatesMessage.
   optional GetUpdatesCallerInfo caller_info = 2;
 
   // Indicates whether related folders should be fetched.
   optional bool fetch_folders = 3 [default = true];
 
-  // The presence of an individual EntitySpecifics extension indicates that the
-  // client requests sync object types associated with that extension.  This
-  // determination depends only on the presence of the extension field, not its
-  // contents -- thus clients should send empty extension messages.  For
-  // backwards compatibility only bookmark objects will be sent to the client
-  // should requested_types not be present.
+  // The presence of an individual EntitySpecifics field indicates that the
+  // client requests sync object types associated with that field.  This
+  // determination depends only on the presence of the field, not its
+  // contents -- thus clients should send empty messages as the field value.
+  // For backwards compatibility only bookmark objects will be sent to the
+  // client should requested_types not be present.
   //
-  // requested_types may contain multiple EntitySpecifics extensions -- in this
+  // requested_types may contain multiple EntitySpecifics fields -- in this
   // event, the server will return items of all the indicated types.
   //
   // requested_types has been deprecated; clients should use
   // |from_progress_marker| instead, which allows more flexibility.
   optional EntitySpecifics requested_types = 4;
 
   // Client-requested limit on the maximum number of updates to return at once.
   // The server may opt to return fewer updates than this amount, but it should
   // not return more.
   optional int32 batch_size = 5;
@@ skipping 243 matching lines @@
   optional string store_birthday = 6;
 
   optional ClientCommand client_command = 7;
   optional ProfilingData profiling_data = 8;
 
   // The data types whose storage has been migrated.  Present when the value of
   // error_code is MIGRATION_DONE.
   repeated int32 migrated_data_type_id = 12;
 };