[Sync] Initial support for encrypting any datatype (no UI hookup yet).

chrome/browser/sync/protocol/sync.proto

 // Copyright (c) 2009 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 "encryption.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:
   //
   //   extend EntitySpecifics {
   //     MyDatatypeSpecifics my_datatype = 32222;
   //   }
   //
@@ skipping 514 matching lines @@
   // Opaque store ID; if it changes, the contents of the client's cache
   // is meaningless to this server.  This happens most typically when
   // you switch from one storage backend instance (say, a test instance)
   // to another (say, the official instance).
   optional string store_birthday = 6;
 
   optional ClientCommand client_command = 7;
   optional ProfilingData profiling_data = 8;
 };