Prevent popunders with the new auto-dismissing dialogs.

chrome/browser/ui/javascript_dialogs/javascript_dialog_mac.cc

Index: chrome/browser/ui/javascript_dialogs/javascript_dialog_mac.cc
diff --git a/chrome/browser/ui/javascript_dialogs/javascript_dialog_mac.cc b/chrome/browser/ui/javascript_dialogs/javascript_dialog_mac.cc
index 119c3ea6378d25571bf17112c74209baeb5b8100..599e9a3fd73c207e4e17a6c5e2b2530109a6bd7a 100644
--- a/chrome/browser/ui/javascript_dialogs/javascript_dialog_mac.cc
+++ b/chrome/browser/ui/javascript_dialogs/javascript_dialog_mac.cc
@@ -4,9 +4,17 @@
 
 #include "chrome/browser/ui/javascript_dialogs/javascript_dialog.h"
 
+#include "chrome/browser/ui/blocked_content/app_modal_dialog_helper.h"
 #include "chrome/browser/ui/browser_dialogs.h"
 #include "chrome/browser/ui/javascript_dialogs/javascript_dialog_cocoa.h"
 #include "chrome/browser/ui/javascript_dialogs/javascript_dialog_views.h"
+#include "content/public/browser/web_contents.h"
+#include "content/public/browser/web_contents_delegate.h"
+
+JavaScriptDialog::JavaScriptDialog(content::WebContents* parent_web_contents) {
+  dialog_helper_.reset(new AppModalDialogHelper(parent_web_contents));
+  parent_web_contents->GetDelegate()->ActivateContents(parent_web_contents);
+}
 
 JavaScriptDialog::~JavaScriptDialog() = default;