fix(textfield): Update label position on value changed via JS

packages/mdc-textfield/README.md

@@ -396,8 +396,9 @@ complicated.
 | --- | --- |
 | addClass(className: string) => void | Adds a class to the root element |
 | removeClass(className: string) => void | Removes a class from the root element |
-| addClassToLabel(className: string) => void | Adds a class to the label element. We recommend you add a conditional check here, and in `removeClassFromLabel` for whether or not the label is present so that the JS component could be used with text fields that don't require a label, such as the full-width text field. |
+| addClassToLabel(className: string) => void | Adds a class to the label element. We recommend you add a conditional check here, in `labelHasClass`, and in `removeClassFromLabel` for whether or not the label is present so that the JS component could be used with text fields that don't require a label, such as the full-width text field. |
 | removeClassFromLabel(className: string) => void | Removes a class from the label element |
+| labelHasClass(className: string) => boolean | Returns true if classname exists for the label element |
 | eventTargetHasClass(target: HTMLElement, className: string) => boolean | Returns true if classname exists for a given target element |
 | registerTextFieldInteractionHandler(evtType: string, handler: EventListener) => void | Registers an event handler on the root element for a given event |
 | deregisterTextFieldInteractionHandler(evtType: string, handler: EventListener) => void | Deregisters an event handler on the root element for a given event |

packages/mdc-textfield/adapter.js

@@ -65,6 +65,13 @@ class MDCTextFieldAdapter {
    */
   removeClassFromLabel(className) {}
 
+  /**
+   * Returns whether or not the label element contains the given class.
+   * @param {string} className
+   * @return {boolean}
+   */
+  labelHasClass(className) {}
+
   /**
    * Sets an attribute on the icon Element.
    * @param {string} name

packages/mdc-textfield/constants.js

@@ -24,6 +24,7 @@ const strings = {
   ICON_SELECTOR: '.mdc-text-field__icon',
   ICON_EVENT: 'MDCTextField:icon',
   BOTTOM_LINE_SELECTOR: '.mdc-text-field__bottom-line',
+  INPUT_PROTO_PROP: 'value',
 };
 
 /** @enum {string} */