Remove third_party/polymer from .gitignore

third_party/polymer/v1_0/components/iron-autogrow-textarea/README.md

-# iron-autogrow-textarea
-
-`iron-autogrow-textarea` is an element containing a textarea that grows in height as more
-lines of input are entered. Unless an explicit height or the `maxRows` property is set, it will
-never scroll.
-
-Example:
-
-    <iron-autogrow-textarea id="a1">
-      <textarea id="t1"></textarea>
-    </iron-autogrow-textarea>
-
-Because the `textarea`'s `value` property is not observable, you should use
-this element's `bind-value` instead for imperative updates. Alternatively, if
-you do set the `textarea`'s `value` imperatively, you must also call `update`
-to notify this element the value has changed.
-
-    Example:
-        /* preferred, using the example HTML above*/
-        a1.bindValue = 'some\ntext';
-
-        /* alternatively, */
-        t1.value = 'some\ntext';
-        a1.update();