[presubmit] Enable readability/namespace linter checking.

tools/shell-utils.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 48 matching lines @@
   fclose(file);
 
   for (int i = file_size; i < *size; i++) {
     chars[i] = chars[i - file_size];
   }
   chars[*size] = 0;
 
   return chars;
 }
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8