Wait for display configuration to finish before suspending

ui/display/chromeos/display_configurator.h

Index: ui/display/chromeos/display_configurator.h
diff --git a/ui/display/chromeos/display_configurator.h b/ui/display/chromeos/display_configurator.h
index 96f93eccae994c35e26f7104df0c8de9a9bd6ba7..309c92331c02b2fcf3de38ea8a4ebe2b96e681db 100644
--- a/ui/display/chromeos/display_configurator.h
+++ b/ui/display/chromeos/display_configurator.h
@@ -224,8 +224,9 @@ class DISPLAY_EXPORT DisplayConfigurator : public NativeDisplayObserver {
 
   // Sets all the displays into pre-suspend mode; usually this means
   // configure them for their resume state. This allows faster resume on
-  // machines where display configuration is slow.
-  void SuspendDisplays();
+  // machines where display configuration is slow. On completion of the display
+  // configuration |callback| is executed.
+  void SuspendDisplays(const ConfigurationCallback& callback);
 
   // Reprobes displays to handle changes made while the system was
   // suspended.