Leverage delite/FormWidget#afterFormResetCallback().

Refs ibm-js/delite#423, #584.

The form reset code for ComboBox, Select, Slider, and Toggle
was apparently added but never tested.  It's unclear if it worked before
or after this change.  The original commits for the form reset handling were:

* Combobox: 59e59c0
* Select: e80ca84
* Slider: c8cf2f0
* Toggle: 6ccd370

Combobox.js

@@ -297,24 +297,18 @@ define([
 					.on("selectstart", false);
 			}
 		},
-
-		attachedCallback: function () {
-			// If the widget is in a form, reset the initial value of the widget
-			// when the form is reset
-			if (this.valueNode.form) {
-				this.on("reset", function () {
-					this.defer(function () {
-						if (this.value !== this.valueNode.value ||
-							// In multiple mode, with no option selected before reset,
-							// valueNode.value is the same but still needs the reinit to get
-							// the correct initial inputNode.value.
-							this.selectionMode === "multiple") {
-							this._initValue();
-						}
-					});
-				}.bind(this), this.valueNode.form);
+
+		afterFormResetCallback: function () {
+			if (this.value !== this.valueNode.value ||
+					// In multiple mode, with no option selected before reset,
+					// valueNode.value is the same but still needs the reinit to get
+					// the correct initial inputNode.value.
+					this.selectionMode === "multiple") {
+				this._initValue();
 			}
-
+		},
+
+		attachedCallback: function () {
 			// Declarative case (list specified declaratively inside the declarative Combobox)
 			if (this.list === this._defaultList) {
 				var list = this.querySelector("d-list");

Select.js

@@ -134,23 +134,17 @@ define([
 		// of selectionMode as provided by delite/Selection.
 
 		template: template,
-
-		attachedCallback: function () {
-			// If the widget is in a form, reset the initial value of the widget
-			// when the form is reset
-			if (this.valueNode.form) {
-				this.on("reset", function () {
-					this.defer(function () {
-						this.valueNode.selectedIndex =
-							this.selectionMode === "single" ?
-							// First option selected in "single" selection mode, and
-							// no option selected in "multiple" mode
-							0 : -1;
-						this.value = this.valueNode.value;
-					});
-				}.bind(this), this.valueNode.form);
-			}
 
+		afterFormResetCallback: function () {
+			this.valueNode.selectedIndex =
+				this.selectionMode === "single" ?
+					// First option selected in "single" selection mode, and
+					// no option selected in "multiple" mode
+					0 : -1;
+			this.value = this.valueNode.value;
+		},
+
+		attachedCallback: function () {
 			// To provide graphic feedback for focus, react to focus/blur events
 			// on the underlying native select. The CSS class is used instead
 			// of the focus pseudo-class because the browsers give the focus

Slider.js

@@ -332,17 +332,6 @@ define([
 			},
 
 			attachedCallback: function () {
-				// if the form is reset, then notify the widget to reposition the handles
-				if (this.valueNode.form) {
-					var self = this;
-					this.on("reset", function () {
-						self.defer(function () {
-							if (this.value !== this.valueNode.value) {
-								this.value = this.valueNode.value;
-							}
-						});
-					}, this.valueNode.form);
-				}
 				// Chrome: avoids text selection of elements when mouse is dragged outside of the Slider.
 				this.onmousedown = function (e) {
 					e.preventDefault();

Toggle.js

@@ -28,14 +28,11 @@ define([
 		value: "on",
 
 		attachedCallback: function () {
-			var initState = this.checked;
-			if (this.valueNode && this.valueNode.form) {
-				this.on("reset", function () {
-					this.defer(function () {
-						this.checked = initState;
-					});
-				}.bind(this), this.valueNode.form);
-			}
+			this._initState = this.checked;
+		},
+
+		afterFormResetCallback: function () {
+			this.checked = this._initState;
 		},
 
 		postRender: function () {