Primary display change notifications.

services/ui/display/platform_screen_delegate.h

Index: services/ui/display/platform_screen_delegate.h
diff --git a/services/ui/display/platform_screen_delegate.h b/services/ui/display/platform_screen_delegate.h
index b326c6a14b7ec7c9f0d1d01c6e4a1c6152b27822..7ad956df8dc66423ee9e5ea33b7a088e9c3d1e8b 100644
--- a/services/ui/display/platform_screen_delegate.h
+++ b/services/ui/display/platform_screen_delegate.h
@@ -34,6 +34,9 @@ class PlatformScreenDelegate {
   virtual void OnDisplayModified(int64_t id,
                                  const ViewportMetrics& metrics) = 0;
 
+  // Called when the primary display is changed.
+  virtual void OnPrimaryDisplayChanged(int64_t primary_display_id) = 0;
+
  protected:
   virtual ~PlatformScreenDelegate() {}
 };