[presubmit] Enable readability/namespace linter checking.

src/string-builder.h

 // Copyright 2014 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_BUILDER_H_
 #define V8_STRING_BUILDER_H_
 
 #include "src/assert-scope.h"
 #include "src/factory.h"
 #include "src/handles.h"
@@ skipping 411 matching lines @@
     DCHECK_EQ(String::ONE_BYTE_ENCODING, encoding_);
     SeqOneByteString::cast(*current_part_)
         ->SeqOneByteStringSet(current_index_++, c);
   } else {
     DCHECK_EQ(String::TWO_BYTE_ENCODING, encoding_);
     SeqTwoByteString::cast(*current_part_)
         ->SeqTwoByteStringSet(current_index_++, c);
   }
   if (current_index_ == part_length_) Extend();
 }
-}
-}  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_STRING_BUILDER_H_