Polymer 2: Two small input fixes

Change-Id: If3f444af8fab9472f4dde9845f3d8e6abdf83138

polygerrit-ui/app/elements/shared/gr-autocomplete/gr-autocomplete.html

@@ -68,7 +68,6 @@ limitations under the License.
         no-label-float
         id="input"
         class$="[[_computeClass(borderless)]]"
-        is="iron-input"
         disabled$="[[disabled]]"
         value="{{text}}"
         placeholder="[[placeholder]]"

polygerrit-ui/app/elements/shared/gr-autocomplete/gr-autocomplete.js

@@ -210,7 +210,8 @@
     },
 
     get _inputElement() {
-      return this.$.input;
+      // Polymer2: this.$ can be undefined when this is first evaluated.
+      return this.$ && this.$.input;
     },
 
     /**