[presubmit] Enable readability/namespace linter checking.

src/base/platform/platform-aix.cc

 // 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.
 
 // Platform specific code for AIX goes here. For the POSIX comaptible parts
 // the implementation is in platform-posix.cc.
 
 #include <pthread.h>
 #include <semaphore.h>
 #include <signal.h>
@@ skipping 221 matching lines @@
   return mprotect(base, size, PROT_NONE) != -1;
 }
 
 
 bool VirtualMemory::ReleaseRegion(void* base, size_t size) {
   return munmap(base, size) == 0;
 }
 
 
 bool VirtualMemory::HasLazyCommits() { return true; }
-}
-}  // namespace v8::base
+}  // namespace base
+}  // namespace v8