[presubmit] Enable readability/namespace linter checking.

test/cctest/gay-shortest.h

 // Copyright 2006-2008 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 23 matching lines @@
 namespace internal {
 
 struct PrecomputedShortest {
   double v;
   const char* representation;
   int decimal_point;
 };
 
 Vector<const PrecomputedShortest> PrecomputedShortestRepresentations();
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // GAY_SHORTEST_H_