[Sync] Move sync/{internal_api,syncable} into syncer namespace

sync/syncable/syncable-inl.h

 // 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.
 
 #ifndef SYNC_SYNCABLE_SYNCABLE_INL_H_
 #define SYNC_SYNCABLE_SYNCABLE_INL_H_
 #pragma once
 
 #include "sync/syncable/entry_kernel.h"
 
+namespace syncer {
 namespace syncable {
 
 template <typename FieldType, FieldType field_index>
 class LessField {
  public:
   inline bool operator() (const syncable::EntryKernel* a,
                           const syncable::EntryKernel* b) const {
     return a->ref(field_index) < b->ref(field_index);
   }
 };
 
 }  // namespace syncable
+}  // namespace syncer
 
 #endif  // SYNC_SYNCABLE_SYNCABLE_INL_H_