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src/lib/dom-api-flush.html

@@ -31,6 +31,8 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
       this._flushGuard = 0;
       this._prepareFlush();
       while (this._debouncers.length && this._flushGuard < this._FLUSH_MAX) {
+        // Avoid using an index in this loop to ensure flush is safe to be
+        // called reentrantly from a debouncer callback being flushed
         while (this._debouncers.length) {
           this._debouncers.shift().complete();
         }