Keep a web dialog window centered over the content area

ui/aura/window.cc

Index: ui/aura/window.cc
diff --git a/ui/aura/window.cc b/ui/aura/window.cc
index ae0778dd8989658a4cf77ceb1f65fd75e8ee6233..b00fd6b7dfd2b83ebb917c27d2d9786b66590b21 100644
--- a/ui/aura/window.cc
+++ b/ui/aura/window.cc
@@ -70,7 +70,8 @@ Window::Window(WindowDelegate* delegate)
       // Don't notify newly added observers during notification. This causes
       // problems for code that adds an observer as part of an observer
       // notification (such as the workspace code).
-      observers_(ObserverList<WindowObserver>::NOTIFY_EXISTING_ONLY) {
+      observers_(ObserverList<WindowObserver>::NOTIFY_EXISTING_ONLY),
+      is_constrained_window_(false) {
   set_target_handler(delegate_);
 }