Use closure-safe name

lib/legacy/class.html

@@ -196,7 +196,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
         // explicitly not calling super._finalizeClass
         static _finalizeClass() {
           // if calling via a subclass that hasn't been generated, pass through to super
-          if (!this.hasOwnProperty('generatedFrom')) {
+          if (!this.hasOwnProperty(window.JSCompiler_renameProperty('generatedFrom', this))) {
             super._finalizeClass();
           } else {
             // interleave properties and observers per behavior and `info`