[presubmit] Enable readability/namespace linter checking.

src/heap/heap.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_HEAP_HEAP_H_
 #define V8_HEAP_HEAP_H_
 
 #include <cmath>
 #include <map>
 
@@ skipping 2700 matching lines @@
   WhatToFind what_to_find_;
   VisitMode visit_mode_;
   List<Object*> object_stack_;
 
   DisallowHeapAllocation no_allocation;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
-}
-}  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_HEAP_HEAP_H_