Print Preview: Focus search box after sign in click

This prevents focus from disappearing (since signing in opens, and
later closes, a new tab).

Bug: 924921
Change-Id: I5fbab1a8bec1b0623fca33dc889f401099499ae4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1654354Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#668570}

chrome/browser/resources/print_preview/ui/destination_dialog.js

@@ -309,6 +309,7 @@ Polymer({
     this.metrics_.record(
         print_preview.Metrics.DestinationSearchBucket.SIGNIN_TRIGGERED);
     print_preview.NativeLayer.getInstance().signIn(false);
+    this.$.searchBox.focus();
   },
 
   /** @private */

chrome/browser/resources/print_preview/ui/print_preview_search_box.js

@@ -38,6 +38,10 @@ Polymer({
     return this.$.searchInput;
   },
 
+  focus: function() {
+    this.$.searchInput.focus();
+  },
+
   /**
    * @param {!CustomEvent<string>} e Event containing the new search.
    * @private