[presubmit] Enable readability/namespace linter checking.

src/x64/lithium-x64.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_X64_LITHIUM_X64_H_
 #define V8_X64_LITHIUM_X64_H_
 
 #include "src/hydrogen.h"
 #include "src/lithium.h"
 #include "src/lithium-allocator.h"
@@ skipping 2846 matching lines @@
   HBasicBlock* current_block_;
   HBasicBlock* next_block_;
   LAllocator* allocator_;
 
   DISALLOW_COPY_AND_ASSIGN(LChunkBuilder);
 };
 
 #undef DECLARE_HYDROGEN_ACCESSOR
 #undef DECLARE_CONCRETE_INSTRUCTION
 
-} }  // namespace v8::int
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_X64_LITHIUM_X64_H_