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

sync/syncable/read_transaction.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_READ_TRANSACTION_H_
 #define SYNC_SYNCABLE_READ_TRANSACTION_H_
 #pragma once
 
 #include "sync/syncable/base_transaction.h"
 
 namespace syncer {
 class ReadTransaction;
-}
-
 namespace syncable {
 
 // Locks db in constructor, unlocks in destructor.
 class ReadTransaction : public BaseTransaction {
  public:
   ReadTransaction(const tracked_objects::Location& from_here,
                   Directory* directory);
 
   virtual ~ReadTransaction();
 
  protected:  // Don't allow creation on heap, except by sync API wrapper.
   friend class syncer::ReadTransaction;
   void* operator new(size_t size) { return (::operator new)(size); }
 
   DISALLOW_COPY_AND_ASSIGN(ReadTransaction);
 };
 
 }  // namespace syncable
+}  // namespace syncer
 
 #endif  // SYNC_SYNCABLE_READ_TRANSACTION_H_