Add more missing closing namespace comments.

third_party/WebKit/Source/core/dom/IntersectionObserverCallback.h

 // Copyright 2016 The Chromium 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 IntersectionObserverCallback_h
 #define IntersectionObserverCallback_h
 
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class ExecutionContext;
 class IntersectionObserver;
 class IntersectionObserverEntry;
 
 class IntersectionObserverCallback : public GarbageCollectedFinalized<IntersectionObserverCallback> {
 public:
     virtual ~IntersectionObserverCallback() {}
     virtual void handleEvent(const HeapVector<Member<IntersectionObserverEntry>>&, IntersectionObserver&) = 0;
     virtual ExecutionContext* executionContext() const = 0;
     DEFINE_INLINE_VIRTUAL_TRACE() { }
 };
 
-}
+} // namespace blink
 
 #endif // IntersectionObserverCallback_h