Update the window labels if they change in overview mode.

ui/aura/window_observer.h

Index: ui/aura/window_observer.h
diff --git a/ui/aura/window_observer.h b/ui/aura/window_observer.h
index ef1259a234d5b99d8e1dd80e3ed51b85fd8c2ff4..b88e2d41077b651e9ae68c384c6e483e292940bd 100644
--- a/ui/aura/window_observer.h
+++ b/ui/aura/window_observer.h
@@ -6,6 +6,7 @@
 #define UI_AURA_WINDOW_OBSERVER_H_
 
 #include "base/basictypes.h"
+#include "base/strings/string16.h"
 #include "ui/aura/aura_export.h"
 
 namespace gfx {
@@ -112,6 +113,9 @@ class AURA_EXPORT WindowObserver {
   virtual void OnWindowRemovingFromRootWindow(Window* window,
                                               Window* new_root) {}
 
+  // Called when the window title has changed.
+  virtual void OnWindowTitleChanged(Window* window) {}
+
  protected:
   virtual ~WindowObserver();