[presubmit] Enable readability/namespace linter checking.

src/snapshot/snapshot.h

 // Copyright 2006-2008 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_SNAPSHOT_SNAPSHOT_H_
 #define V8_SNAPSHOT_SNAPSHOT_H_
 
 #include "src/snapshot/serialize.h"
 
 namespace v8 {
@@ skipping 71 matching lines @@
     return kStartupDataOffset + startup_length;
   }
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(Snapshot);
 };
 
 #ifdef V8_USE_EXTERNAL_STARTUP_DATA
 void SetSnapshotFromFile(StartupData* snapshot_blob);
 #endif
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_SNAPSHOT_SNAPSHOT_H_