[Sync] Rename csync namespace to syncer

sync/engine/syncproto_unittest.cc

 // 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.
 
 #include "sync/engine/syncproto.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-namespace csync {
+namespace syncer {
 
 class SyncProtoTest : public testing::Test {
 };
 
 TEST_F(SyncProtoTest, ProtocolVersionPresent) {
   ClientToServerMessage csm;
   EXPECT_TRUE(csm.has_protocol_version());
 }
 
-}  // namespace csync
+}  // namespace syncer