feat(formController): add $setUntouched to propagate untouched state

Closes #9050

Author: shahata

src/ng/directive/form.js

@@ -230,6 +230,25 @@ function FormController(element, attrs, $scope, $animate) {
     });
   };
 
+  /**
+   * @ngdoc method
+   * @name form.FormController#$setUntouched
+   *
+   * @description
+   * Sets the form to its untouched state.
+   *
+   * This method can be called to remove the 'ng-touched' class and set the form controls to their
+   * untouched state (ng-untouched class).
+   *
+   * Setting a form controls back to their untouched state is often useful when setting the form
+   * back to its pristine state.
+   */
+  form.$setUntouched = function () {
+    forEach(controls, function(control) {
+      control.$setUntouched();
+    });
+  };
+
   /**
    * @ngdoc method
    * @name form.FormController#$setSubmitted

test/ng/directive/formSpec.js

@@ -750,6 +750,38 @@ describe('form', function() {
     });
   });
 
+  describe('$setUntouched', function () {
+    it('should trigger setUntouched on form controls', function() {
+      var form = $compile(
+          '<form name="myForm">' +
+            '<input name="alias" type="text" ng-model="name" />' +
+          '</form>')(scope);
+      scope.$digest();
+
+      scope.myForm.alias.$setTouched();
+      expect(scope.myForm.alias.$touched).toBe(true);
+      scope.myForm.$setUntouched();
+      expect(scope.myForm.alias.$touched).toBe(false);
+      dealoc(form);
+    });
+
+    it('should trigger setUntouched on form controls with nested forms', function() {
+      var form = $compile(
+          '<form name="myForm">' +
+            '<div class="ng-form" name="childForm">' +
+              '<input name="alias" type="text" ng-model="name" />' +
+            '</div>' +
+          '</form>')(scope);
+      scope.$digest();
+
+      scope.myForm.childForm.alias.$setTouched();
+      expect(scope.myForm.childForm.alias.$touched).toBe(true);
+      scope.myForm.$setUntouched();
+      expect(scope.myForm.childForm.alias.$touched).toBe(false);
+      dealoc(form);
+    });
+  });
+
   describe('$setSubmitted', function() {
     beforeEach(function() {
       doc = $compile(