Update listener_helpers

Runtime/animation/listener_helpers.mixin.gen.cs

         }
 
         public override void removeListener(VoidCallback listener) {
-            this._listeners.Remove(listener);
-            this.didUnregisterListener();
+            bool removed = this._listeners.Remove(listener);
+            if(removed) {
+                this.didUnregisterListener();
+            }
         }
 
         public void notifyListeners() {
         }
 
         public override void removeListener(VoidCallback listener) {
-            this._listeners.Remove(listener);
-            this.didUnregisterListener();
+            bool removed = this._listeners.Remove(listener);
+            if(removed) {
+                this.didUnregisterListener();
+            }
         }
 
         public void notifyListeners() {
         }
 
         public override void removeStatusListener(AnimationStatusListener listener) {
-            this._statusListeners.Remove(listener);
-            this.didUnregisterListener();
+            bool removed = this._statusListeners.Remove(listener);
+            if(removed) {
+                this.didUnregisterListener();
+            }
         }
 
         public void notifyStatusListeners(AnimationStatus status) {
         }
 
         public override void removeStatusListener(AnimationStatusListener listener) {
-            this._statusListeners.Remove(listener);
-            this.didUnregisterListener();
+            bool removed = this._statusListeners.Remove(listener);
+            if(removed) {
+                this.didUnregisterListener();
+            }
         }
 
         public void notifyStatusListeners(AnimationStatus status) {
         }
 
         public override void removeStatusListener(AnimationStatusListener listener) {
-            this._statusListeners.Remove(listener);
-            this.didUnregisterListener();
+            bool removed = this._statusListeners.Remove(listener);
+            if(removed) {
+                this.didUnregisterListener();
+            }
         }
 
         public void notifyStatusListeners(AnimationStatus status) {

Runtime/animation/listener_helpers.mixin.njk

         }
 
         public override void removeListener(VoidCallback listener) {
-            this._listeners.Remove(listener);
-            this.didUnregisterListener();
+            bool removed = this._listeners.Remove(listener);
+            if(removed) {
+                this.didUnregisterListener();
+            }
         }
 
         public void notifyListeners() {
         }
 
         public override void removeStatusListener(AnimationStatusListener listener) {
-            this._statusListeners.Remove(listener);
-            this.didUnregisterListener();
+            bool removed = this._statusListeners.Remove(listener);
+            if(removed) {
+                this.didUnregisterListener();
+            }
         }
 
         public void notifyStatusListeners(AnimationStatus status) {

Runtime/foundation/node.mixin.gen.cs

         
         static readonly Dictionary<_DependencyList, WeakReference> _canonicalObjects =
             new Dictionary<_DependencyList, WeakReference>();
-
-        public bool pureWidget { get; set; } // pure = false, if canonicalEquals should not be used.
+        
+        public bool pureWidget { get; set; } // if canonicalEquals should not be used.
 
         public override bool Equals(object obj) {
             if (ReferenceEquals(null, obj)) {

Runtime/rendering/object.mixin.gen.cs

             get { return this._childCount; }
         }
 
-        public new bool debugValidateChild(RenderObject child) {
+        public bool debugValidateChild(RenderObject child) {
             D.assert(() => {
                 if (!(child is ChildType)) {
                     throw new UIWidgetsError(