[presubmit] Enable readability/namespace linter checking.

src/splay-tree.h

 // Copyright 2010 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_SPLAY_TREE_H_
 #define V8_SPLAY_TREE_H_
 
 #include "src/allocation.h"
 
 namespace v8 {
@@ skipping 180 matching lines @@
   template <class Callback>
   void ForEachNode(Callback* callback);
 
   Node* root_;
   AllocationPolicy allocator_;
 
   DISALLOW_COPY_AND_ASSIGN(SplayTree);
 };
 
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_SPLAY_TREE_H_