[presubmit] Enable readability/namespace linter checking.

src/ppc/lithium-gap-resolver-ppc.h

 // Copyright 2014 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_PPC_LITHIUM_GAP_RESOLVER_PPC_H_
 #define V8_PPC_LITHIUM_GAP_RESOLVER_PPC_H_
 
 #include "src/lithium.h"
 
 namespace v8 {
@@ skipping 34 matching lines @@
 
   LCodeGen* cgen_;
 
   // List of moves not yet resolved.
   ZoneList<LMoveOperands> moves_;
 
   int root_index_;
   bool in_cycle_;
   LOperand* saved_destination_;
 };
-}
-}  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_PPC_LITHIUM_GAP_RESOLVER_PPC_H_