Set active_dialog_ before showing it, since showing a dialog can sometimes...

chrome/browser/app_modal_dialog_queue.cc

Index: chrome/browser/app_modal_dialog_queue.cc
===================================================================
--- chrome/browser/app_modal_dialog_queue.cc	(revision 30367)
+++ chrome/browser/app_modal_dialog_queue.cc	(working copy)
@@ -30,6 +30,8 @@
 }
 
 void AppModalDialogQueue::ShowModalDialog(AppModalDialog* dialog) {
+  // Set active_dialog_ before showing it, because ShowModalDialog can wind up
+  // calling ShowNextDialog in some cases, which will change active_dialog_.
+  active_dialog_ = dialog;
   dialog->ShowModalDialog();
-  active_dialog_ = dialog;
 }