fix: on-change event in shadowRoot

iron-autogrow-textarea.d.ts

@@ -130,6 +130,7 @@ interface IronAutogrowTextareaElement extends Polymer.Element, Polymer.IronValid
   _constrain(tokens: any): any;
   _valueForMirror(): any;
   _updateCached(): void;
+  _onChange(event: any): void;
 }
 
 interface HTMLElementTagNameMap {

iron-autogrow-textarea.html

@@ -112,7 +112,8 @@
         disabled$="[[disabled]]"
         rows$="[[rows]]"
         minlength$="[[minlength]]"
-        maxlength$="[[maxlength]]"></textarea>
+        maxlength$="[[maxlength]]"
+        on-change="_onChange"></textarea>
     </div>
   </template>
 </dom-module>
@@ -347,5 +348,18 @@
     _updateCached: function() {
       this.$.mirror.innerHTML = this._constrain(this.tokens);
     },
+
+    _onChange: function(event) {
+      // In the Shadow DOM, the `change` event is not leaked into the
+      // ancestor tree, so we must do this manually.
+      // See
+      // https://w3c.github.io/webcomponents/spec/shadow/#events-that-are-not-leaked-into-ancestor-trees.
+      if (this.shadowRoot) {
+        this.fire(
+            event.type,
+            {sourceEvent: event},
+            {node: this, bubbles: event.bubbles, cancelable: event.cancelable});
+      }
+    },
   });
 </script>