MD WebUI: Improve tab focus behavior for toolbar search field

ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.js

Index: ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.js
diff --git a/ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.js b/ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.js
index aac426820c43e00e97956025673933bea7ae198f..1729ff9d062bb8cb55020f9a0e78aa98efa59231 100644
--- a/ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.js
+++ b/ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.js
@@ -25,6 +25,15 @@ Polymer({
     'tap': 'showSearch_',
   },
 
+  /**
+   * @param {boolean} narrow
+   * @return {number}
+   * @private
+   */
+  computeIconTabIndex_: function(narrow) {
+    return narrow ? 0 : -1;
+  },
+
   /** @private */
   onInputBlur_: function() {
     if (!this.hasSearchText)
@@ -32,6 +41,16 @@ Polymer({
   },
 
   /**
+   * Expand the search field when a key is pressed with it focused. This ensures
+   * it can be used correctly by tab-focusing. 'keypress' is used instead of
+   * 'keydown' to avoid expanding on non-text keys (shift, escape, etc).
+   * @private
+   */
+  onSearchTermKeypress_: function() {
+    this.showingSearch = true;
+  },
+
+  /**
    * @param {Event} e
    * @private
    */