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

sync/syncable/syncable_id.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/syncable/syncable_id.h"
 
 #include <iosfwd>
 
 #include "base/values.h"
 
 using std::ostream;
 using std::string;
 
+namespace syncer {
 namespace syncable {
 
 ostream& operator<<(ostream& out, const Id& id) {
   out << id.s_;
   return out;
 }
 
 StringValue* Id::ToValue() const {
   return Value::CreateStringValue(s_);
 }
@@ skipping 37 matching lines @@
   Id id;
   id.s_.clear();
   return id;
 }
 
 Id GetNullId() {
   return Id();  // Currently == root.
 }
 
 }  // namespace syncable
+}  // namespace syncer