[presubmit] Enable readability/namespace linter checking.

src/heap/gc-idle-time-handler.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.
 
 #include "src/heap/gc-idle-time-handler.h"
 
 #include "src/flags.h"
 #include "src/heap/gc-tracer.h"
 #include "src/utils.h"
 
@@ skipping 168 matching lines @@
   }
 
   if (!FLAG_incremental_marking || heap_state.incremental_marking_stopped) {
     return GCIdleTimeAction::Done();
   }
 
   return GCIdleTimeAction::IncrementalStep();
 }
 
 
-}
-}
+}  // namespace internal
+}  // namespace v8