[presubmit] Enable readability/namespace linter checking.

src/string-search.h

 // Copyright 2011 the V8 project 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 V8_STRING_SEARCH_H_
 #define V8_STRING_SEARCH_H_
 
 #include "src/isolate.h"
 #include "src/vector.h"
 
@@ skipping 545 matching lines @@
 // for each search.
 template <typename SubjectChar, typename PatternChar>
 int SearchString(Isolate* isolate,
                  Vector<const SubjectChar> subject,
                  Vector<const PatternChar> pattern,
                  int start_index) {
   StringSearch<PatternChar, SubjectChar> search(isolate, pattern);
   return search.Search(subject, start_index);
 }
 
-}}  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_STRING_SEARCH_H_