[presubmit] Enable readability/namespace linter checking.

src/fast-dtoa.h

 // Copyright 2011 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_FAST_DTOA_H_
 #define V8_FAST_DTOA_H_
 
 #include "src/vector.h"
 
 namespace v8 {
@@ skipping 39 matching lines @@
 //     If there are two values that are equally close, then FastDtoa returns
 //     false.
 // For both modes the buffer must be large enough to hold the result.
 bool FastDtoa(double d,
               FastDtoaMode mode,
               int requested_digits,
               Vector<char> buffer,
               int* length,
               int* decimal_point);
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_FAST_DTOA_H_