[presubmit] Enable readability/namespace linter checking.

src/libplatform/default-platform.cc

 // 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.
 
 #include "src/libplatform/default-platform.h"
 
 #include <algorithm>
 #include <queue>
 
 #include "src/base/logging.h"
@@ skipping 150 matching lines @@
 }
 
 
 bool DefaultPlatform::IdleTasksEnabled(Isolate* isolate) { return false; }
 
 
 double DefaultPlatform::MonotonicallyIncreasingTime() {
   return base::TimeTicks::HighResolutionNow().ToInternalValue() /
          static_cast<double>(base::Time::kMicrosecondsPerSecond);
 }
-} }  // namespace v8::platform
+}  // namespace platform
+}  // namespace v8