[presubmit] Enable readability/namespace linter checking.

src/base/platform/platform-linux.cc

 // 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.
 
 // Platform-specific code for Linux goes here. For the POSIX-compatible
 // parts, the implementation is in platform-posix.cc.
 
 #include <pthread.h>
 #include <semaphore.h>
 #include <signal.h>
@@ skipping 370 matching lines @@
   __lsan_unregister_root_region(base, size);
 #endif
   return munmap(base, size) == 0;
 }
 
 
 bool VirtualMemory::HasLazyCommits() {
   return true;
 }
 
-} }  // namespace v8::base
+}  // namespace base
+}  // namespace v8