RefCounted types should not have public destructors, delegate cleanup

chrome/browser/history/history.h

Index: chrome/browser/history/history.h
diff --git a/chrome/browser/history/history.h b/chrome/browser/history/history.h
index 1d7678947613aaad711765dc7d0774b6e54d58e3..46c56f2eddb00d0434778288f9556887af3d44be 100644
--- a/chrome/browser/history/history.h
+++ b/chrome/browser/history/history.h
@@ -249,8 +249,6 @@ class HistoryService : public CancelableRequestProvider,
   // should handle this appropriately.
   class URLEnumerator {
    public:
-    virtual ~URLEnumerator() {}
-
     // Indicates that a URL is available. There will be exactly one call for
     // every URL in history.
     virtual void OnURL(const GURL& url) = 0;
@@ -259,6 +257,9 @@ class HistoryService : public CancelableRequestProvider,
     // more callbacks made. This call is guaranteed to occur, even if there are
     // no URLs. If all URLs were iterated, success will be true.
     virtual void OnComplete(bool success) = 0;
+
+   protected:
+    virtual ~URLEnumerator() {}
   };
 
   // Enumerate all URLs in history. The given iterator will be owned by the