feat(ngForm): allow forms to be manually validated

lib/directive/ng_control.dart

@@ -52,6 +52,15 @@ abstract class NgControl implements AttachAware, DetachAware {
     _parentControl..removeStates(this)..removeControl(this);
   }
 
+  /**
+   * Revalidates the model by performing validations on each of the child controls.
+   */
+  void validate() {
+    _controls.forEach((control) {
+      control.validate();
+    });
+  }
+
   /**
     * Resets the form and inner models to their pristine state.
     */
@@ -339,7 +348,9 @@ class NgNullControl implements NgControl {
   void addInfoState(NgControl control, String state) {}
   void removeInfoState(NgControl control, String state) {}
 
+  void validate() {}
   void reset() {}
+
   void attach() {}
   void detach() {}
 

test/directive/ng_form_spec.dart

@@ -553,6 +553,54 @@ void main() {
         expect(form).not.toHaveClass('ng-required-invalid');
       });
 
+      it('should validate all the models when form.validate() is called',
+        (TestBed _, Scope scope) {
+
+        scope.context['required'] = true;
+        var formElement = _.compile('<form name="myForm">'
+                    '<input type="text" ng-model="one" probe="a" required />'
+                    '<input type="text" ng-model="two" probe="b" required />'
+                    '<input type="text" ng-model="three" probe="c" required />'
+                  '</form>');
+        scope.apply();
+
+        NgForm form = _.rootScope.context['myForm'];
+
+        var one = _.rootScope.context['a'].directive(NgModel);
+        var inputOne = one.element.node;
+
+        var two = _.rootScope.context['b'].directive(NgModel);
+        var inputTwo = two.element.node;
+
+        var three = _.rootScope.context['c'].directive(NgModel);
+        var inputThree = three.element.node;
+
+        expect(form.invalid).toBe(true);
+        expect(one.invalid).toBe(true);
+        expect(two.invalid).toBe(true);
+        expect(three.invalid).toBe(true);
+
+        one.viewValue = 'something';
+        expect(one.invalid).toBe(true);
+
+        form.validate();
+
+        expect(one.invalid).toBe(false);
+        expect(two.invalid).toBe(true);
+        expect(three.invalid).toBe(true);
+        expect(form.invalid).toBe(true);
+
+        two.viewValue = 'something else';
+        three.viewValue = 'something more';
+
+        form.validate();
+
+        expect(one.invalid).toBe(false);
+        expect(two.invalid).toBe(false);
+        expect(three.invalid).toBe(false);
+        expect(form.invalid).toBe(false);
+      });
+
       it('should re-validate itself when validators are toggled on and off',
         (TestBed _, Scope scope) {