update elements and fix some bugs

lib/iron_validatable_behavior.dart

 // DO NOT EDIT: auto-generated with `pub run custom_element_apigen:update`
 
 /// Dart API for the polymer element `iron_validatable_behavior`.
 @HtmlImport('iron_validatable_behavior_nodart.html')
 library polymer_elements.lib.src.iron_validatable_behavior.iron_validatable_behavior;
 
 import 'dart:html';
 import 'dart:js' show JsArray, JsObject;
 import 'package:web_components/web_components.dart';
 import 'package:polymer_interop/polymer_interop.dart';
 import 'iron_meta.dart';
 
-/// Use `Polymer.IronValidatableBehavior` to implement an element that validates user input.
+/// `Use Polymer.IronValidatableBehavior` to implement an element that validates user input.
+/// Use the related `Polymer.IronValidatorBehavior` to add custom validation logic to an iron-input.
+///
+/// By default, an `<iron-form>` element validates its fields when the user presses the submit button.
+/// To validate a form imperatively, call the form's `validate()` method, which in turn will
+/// call `validate()` on all its children. By using `Polymer.IronValidatableBehavior`, your
+/// custom element will get a public `validate()`, which
+/// will return the validity of the element, and a corresponding `invalid` attribute,
+/// which can be used for styling.
+///
+/// To implement the custom validation logic of your element, you must override
+/// the protected `_getValidity()` method of this behaviour, rather than `validate()`.
+/// See [this](https://github.com/PolymerElements/iron-form/blob/master/demo/simple-element.html)
+/// for an example.
 ///
 /// ### Accessibility
 ///
 /// Changing the `invalid` property, either manually or by calling `validate()` will update the
 /// `aria-invalid` attribute.
 @BehaviorProxy(const ['Polymer', 'IronValidatableBehavior'])
 abstract class IronValidatableBehavior implements CustomElementProxyMixin {
 
   /// True if the last call to `validate` is invalid.
   bool get invalid => jsElement[r'invalid'];
@@ skipping 11 matching lines @@
       jsElement.callMethod('hasValidator', []);
 
   /// Returns true if the `value` is valid, and updates `invalid`. If you want
   /// your element to have custom validation logic, do not override this method;
   /// override `_getValidity(value)` instead.
   /// [value]: The value to be validated. By default, it is passed
   ///     to the validator's `validate()` function, if a validator is set.
   bool validate(value) =>
       jsElement.callMethod('validate', [value]);
 }