Fix focus issue with autocomplete

Due to asynchronous event handling, sometimes the _focused flag is not
properly set to 'true' even when the input is focused. With this change,
the _focused flag is set to true on keydown in the input.

Also sets a parameter on the cursor-manager for better UX.

Bug: Issue 4950
Change-Id: Ib53942f0d1ff86351bdbd33770696e1bb3e029ca

polygerrit-ui/app/elements/change/gr-account-list/gr-account-list.js

@@ -91,6 +91,7 @@
     _handleRemove: function(e) {
       var toRemove = e.detail.account;
       this._removeAccount(toRemove);
+      this.$.entry.focus();
     },
 
     _removeAccount: function(toRemove) {
@@ -105,7 +106,6 @@
         }
         if (matches) {
           this.splice('accounts', i, 1);
-          this.$.entry.focus();
           return;
         }
       }

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

@@ -73,6 +73,7 @@ limitations under the License.
         id="cursor"
         index="{{_index}}"
         cursor-target-class="selected"
+        scroll-behavior="keep-visible"
         stops="[[_getSuggestionElems(_suggestions)]]"></gr-cursor-manager>
   </template>
   <script src="gr-autocomplete.js"></script>

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

@@ -199,6 +199,7 @@
     },
 
     _handleInputKeydown: function(e) {
+      this._focused = true;
       switch (e.keyCode) {
         case 38: // Up
           e.preventDefault();