Add notifyDomChange back to dom-if & dom-repeat to match P1.

Author: kevinpschaaf

lib/elements/dom-if.js

@@ -63,8 +63,16 @@ class DomIfBase extends PolymerElement {
       restamp: {
         type: Boolean,
         observer: '__debounceRender'
-      }
+      },
 
+      /**
+       * When the global `legacyOptimizations` setting is used, setting
+       * `notifyDomChange: true` will enable firing `dom-change` events on this
+       * element.
+       */
+      notifyDomChange: {
+        type: Boolean
+      }
     };
 
   }
@@ -244,7 +252,7 @@ class DomIfBase extends PolymerElement {
       this.__teardownInstance();
     }
     this._showHideChildren();
-    if (!legacyOptimizations && this.if != this._lastIf) {
+    if ((!legacyOptimizations || this.notifyDomChange) && this.if != this._lastIf) {
       this.dispatchEvent(new CustomEvent('dom-change', {
         bubbles: true,
         composed: true

lib/elements/dom-repeat.js

@@ -276,6 +276,15 @@ export class DomRepeat extends domRepeatBase {
       _targetFrameTime: {
         type: Number,
         computed: '__computeFrameTime(targetFramerate)'
+      },
+
+      /**
+       * When the global `legacyOptimizations` setting is used, setting
+       * `notifyDomChange: true` will enable firing `dom-change` events on this
+       * element.
+       */
+      notifyDomChange: {
+        type: Boolean
       }
 
     };
@@ -546,7 +555,7 @@ export class DomRepeat extends domRepeatBase {
     // Set rendered item count
     this._setRenderedItemCount(this.__instances.length);
     // Notify users
-    if (!legacyOptimizations) {
+    if (!legacyOptimizations || this.notifyDomChange) {
       this.dispatchEvent(new CustomEvent('dom-change', {
         bubbles: true,
         composed: true