[presubmit] Enable readability/namespace linter checking.

src/double.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_DOUBLE_H_
 #define V8_DOUBLE_H_
 
 #include "src/diy-fp.h"
 
 namespace v8 {
@@ skipping 186 matching lines @@
     if (exponent == kDenormalExponent && (significand & kHiddenBit) == 0) {
       biased_exponent = 0;
     } else {
       biased_exponent = static_cast<uint64_t>(exponent + kExponentBias);
     }
     return (significand & kSignificandMask) |
         (biased_exponent << kPhysicalSignificandSize);
   }
 };
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_DOUBLE_H_