[presubmit] Enable readability/namespace linter checking.

src/libplatform/default-platform.h

 // Copyright 2013 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_LIBPLATFORM_DEFAULT_PLATFORM_H_
 #define V8_LIBPLATFORM_DEFAULT_PLATFORM_H_
 
 #include <functional>
 #include <map>
 #include <queue>
@@ skipping 50 matching lines @@
   typedef std::pair<double, Task*> DelayedEntry;
   std::map<v8::Isolate*,
            std::priority_queue<DelayedEntry, std::vector<DelayedEntry>,
                                std::greater<DelayedEntry> > >
       main_thread_delayed_queue_;
 
   DISALLOW_COPY_AND_ASSIGN(DefaultPlatform);
 };
 
 
-} }  // namespace v8::platform
+}  // namespace platform
+}  // namespace v8
 
 
 #endif  // V8_LIBPLATFORM_DEFAULT_PLATFORM_H_