Added an ActivationReason parameter to ActivationChangeObserver::OnWindowActivated(...).

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index cb46540be67024994d76283a444bec82bd950b68..fe5fdd822320e002b37e589820ed484ade308527 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -617,8 +617,10 @@ class ASH_EXPORT Shell : public SystemModalContainerEventFilterDelegate,
   void OnEvent(ui::Event* event) override;
 
   // Overridden from aura::client::ActivationChangeObserver:
-  void OnWindowActivated(aura::Window* gained_active,
-                         aura::Window* lost_active) override;
+  void OnWindowActivated(
+      aura::client::ActivationChangeObserver::ActivationReason reason,
+      aura::Window* gained_active,
+      aura::Window* lost_active) override;
 
   static Shell* instance_;