[presubmit] Enable readability/namespace linter checking.

src/hashmap.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_HASHMAP_H_
 #define V8_HASHMAP_H_
 
 #include "src/allocation.h"
 #include "src/base/bits.h"
 #include "src/base/logging.h"
@@ skipping 332 matching lines @@
   Iterator end() const { return Iterator(this, NULL); }
   Iterator find(Key* key, bool insert = false,
                 AllocationPolicy allocator = AllocationPolicy()) {
     if (insert) {
       return Iterator(this, this->LookupOrInsert(key, key->Hash(), allocator));
     }
     return Iterator(this, this->Lookup(key, key->Hash()));
   }
 };
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_HASHMAP_H_