Switched sync protobufs to use "heavy" protobufs.

chrome/browser/sync/protocol/encryption.proto

 // Copyright (c) 2010 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.
 //
 // Common sync protocol for encrypted data.
 
 syntax = "proto2";
 
-option optimize_for = LITE_RUNTIME;
+// TODO(akalin): Re-enable this once LITE_RUNTIME supports preserving
+// unknown fields.
+
+// option optimize_for = LITE_RUNTIME;
 
 package sync_pb;
 
 // Encrypted sync data consists of two parts: a key name and a blob. Key name is
 // the name of the key that was used to encrypt blob and blob is encrypted data
 // itself.
 //
 // The reason we need to keep track of the key name is that a sync user can
 // change their passphrase (and thus their encryption key) at any time. When
 // that happens, we make a best effort to reencrypt all nodes with the new
 // passphrase, but since we don't have transactions on the server-side, we
 // cannot garantee that every node will be reencrypted. As a workaround, we keep
 // track of all keys, assign each key a name (by using that key to encrypt a
 // well known string) and keep track of which key was used to encrypt each node.
 message EncryptedData {
   optional string key_name = 1;
   optional string blob = 2;
 };