Add a JavaScript dialog tab helper.

chrome/browser/ui/tab_helpers.cc

Index: chrome/browser/ui/tab_helpers.cc
diff --git a/chrome/browser/ui/tab_helpers.cc b/chrome/browser/ui/tab_helpers.cc
index be248129d3d19090e116ad39f43469e5f174906c..20392e8bb5efa089e983c7dc87da5781237ffb20 100644
--- a/chrome/browser/ui/tab_helpers.cc
+++ b/chrome/browser/ui/tab_helpers.cc
@@ -34,6 +34,7 @@
 #include "chrome/browser/ui/autofill/chrome_autofill_client.h"
 #include "chrome/browser/ui/blocked_content/popup_blocker_tab_helper.h"
 #include "chrome/browser/ui/find_bar/find_tab_helper.h"
+#include "chrome/browser/ui/javascript_dialogs/javascript_dialog_tab_helper.h"
 #include "chrome/browser/ui/navigation_correction_tab_observer.h"
 #include "chrome/browser/ui/passwords/manage_passwords_ui_controller.h"
 #include "chrome/browser/ui/pdf/chrome_pdf_web_contents_helper_client.h"
@@ -167,6 +168,7 @@ void TabHelpers::AttachTabHelpers(WebContents* web_contents) {
                             web_contents->GetBrowserContext())).get());
   HistoryTabHelper::CreateForWebContents(web_contents);
   InfoBarService::CreateForWebContents(web_contents);
+  JavaScriptDialogTabHelper::CreateForWebContents(web_contents);
   NavigationCorrectionTabObserver::CreateForWebContents(web_contents);
   NavigationMetricsRecorder::CreateForWebContents(web_contents);
   chrome::InitializePageLoadMetricsForWebContents(web_contents);