[presubmit] Enable readability/namespace linter checking.

src/api.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_API_H_
 #define V8_API_H_
 
 #include "include/v8-testing.h"
 #include "src/contexts.h"
 #include "src/factory.h"
@@ skipping 624 matching lines @@
  public:
   static v8::Testing::StressType stress_type() { return stress_type_; }
   static void set_stress_type(v8::Testing::StressType stress_type) {
     stress_type_ = stress_type;
   }
 
  private:
   static v8::Testing::StressType stress_type_;
 };
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_API_H_