Objects that derive from RefCounted/RefCountedThreadSafe should not have public dtors.

BUG=none
TEST=compiles


Review URL: http://codereview.chromium.org/9997007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@131088 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/base/single_thread_task_runner.h b/base/single_thread_task_runner.h
index 93f694e..c87e5f7 100644
--- a/base/single_thread_task_runner.h
+++ b/base/single_thread_task_runner.h
@@ -26,11 +26,14 @@
 //     order that must be run only from the thread the
 //     SingleThreadTaskRunner was created on.
 class BASE_EXPORT SingleThreadTaskRunner : public SequencedTaskRunner {
-public:
+ public:
   // A more explicit alias to RunsTasksOnCurrentThread().
   bool BelongsToCurrentThread() const {
     return RunsTasksOnCurrentThread();
   }
+
+ protected:
+  virtual ~SingleThreadTaskRunner() {}
 };
 
 }  // namespace base