[presubmit] Enable readability/namespace linter checking.

src/hydrogen.h

 // Copyright 2012 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_HYDROGEN_H_
 #define V8_HYDROGEN_H_
 
 #include "src/accessors.h"
 #include "src/allocation.h"
 #include "src/ast.h"
@@ skipping 3055 matching lines @@
   }
   ~NoObservableSideEffectsScope() {
     builder_->graph()->DecrementInNoSideEffectsScope();
   }
 
  private:
   HGraphBuilder* builder_;
 };
 
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_HYDROGEN_H_