[presubmit] Enable readability/namespace linter checking.

src/hydrogen-types.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 HYDROGEN_TYPES_H_
 #define HYDROGEN_TYPES_H_
 
 #include <climits>
 #include <iosfwd>
 
@@ skipping 68 matching lines @@
   // Make sure type fits in int16.
   STATIC_ASSERT(LAST_KIND < (1 << (CHAR_BIT * sizeof(int16_t))));
 
   explicit HType(Kind kind) : kind_(kind) { }
 
   int16_t kind_;
 };
 
 
 std::ostream& operator<<(std::ostream& os, const HType& t);
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // HYDROGEN_TYPES_H_