history: add a browser test for confirm dialog focus regression.

chrome/test/data/webui/history_browsertest.js

Index: chrome/test/data/webui/history_browsertest.js
diff --git a/chrome/test/data/webui/history_browsertest.js b/chrome/test/data/webui/history_browsertest.js
index 36cad2925c738ed97ff9509591c3a51d6c41b961..b19f10f9e13d03d8f36ef880adab163177199218 100644
--- a/chrome/test/data/webui/history_browsertest.js
+++ b/chrome/test/data/webui/history_browsertest.js
@@ -873,6 +873,13 @@ TEST_F('HistoryWebUIRealBackendTest', 'leftRightChangeFocus', function() {
   testDone();
 });
 
+TEST_F('HistoryWebUIRealBackendTest', 'alertOverlayHasFocus', function() {
+  document.querySelector('input[type=checkbox]').click();
+  $('remove-selected').click();
+  assert($('alertOverlay').contains(document.activeElement));
+  testDone();
+});
+
 /**
  * Fixture for History WebUI testing when deletions are prohibited.
  * @extends {HistoryWebUIRealBackendTest}