Valgrind cleanliness, part 4: Delete CounterMap on exit.

This fixes 2 leaks, returning 112 bytes of lost memory.

As an additional bonus, a useless check has been removed (no need to check for
NULL before a delete).

Review URL: https://chromiumcodereview.appspot.com/9864029

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11152 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/d8.cc

@@ -986,8 +986,8 @@ void Shell::OnExit() {
     printf("+--------------------------------------------+-------------+\n");
     delete [] counters;
   }
-  if (counters_file_ != NULL)
-    delete counters_file_;
+  delete counters_file_;
+  delete counter_map_;
 }
 #endif  // V8_SHARED