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

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index fb61b55893a6e7c274829105a75bea1f9966b97d..8393cda6f98449a3e0b06a32a869033797fd1305 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -1177,8 +1177,10 @@ void Shell::OnEvent(ui::Event* event) {
 ////////////////////////////////////////////////////////////////////////////////
 // Shell, aura::client::ActivationChangeObserver implementation:
 
-void Shell::OnWindowActivated(aura::Window* gained_active,
-                              aura::Window* lost_active) {
+void Shell::OnWindowActivated(
+    aura::client::ActivationChangeObserver::ActivationReason reason,
+    aura::Window* gained_active,
+    aura::Window* lost_active) {
   if (gained_active)
     target_root_window_ = gained_active->GetRootWindow();
 }