Fix browser launch on the login screen.

ui/web_dialogs/web_dialog_delegate.h

Index: ui/web_dialogs/web_dialog_delegate.h
diff --git a/ui/web_dialogs/web_dialog_delegate.h b/ui/web_dialogs/web_dialog_delegate.h
index ccfd26ef98287f8e292653cf30d97d2d59d672b5..898b04513d416765bead45344e6eb560028e3dbd 100644
--- a/ui/web_dialogs/web_dialog_delegate.h
+++ b/ui/web_dialogs/web_dialog_delegate.h
@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "base/strings/string16.h"
+#include "content/public/browser/web_contents_delegate.h"
 #include "ui/base/ui_base_types.h"
 #include "ui/base/window_open_disposition.h"
 #include "ui/web_dialogs/web_dialogs_export.h"
@@ -128,6 +129,10 @@ class WEB_DIALOGS_EXPORT WebDialogDelegate {
                                     const gfx::Rect& initial_pos,
                                     bool user_gesture);
 
+  // A callback to control whether a WebContents will be created. Returns
+  // false to disallow the creation. Return true to use the default handler.
+  virtual bool HandleShouldCreateWebContents();
+
   // Stores the dialog bounds.
   virtual void StoreDialogSize(const gfx::Size& dialog_size) {}