Make aura::clients take Window instead of RootWindow

ui/aura/client/default_activation_client.h

Index: ui/aura/client/default_activation_client.h
diff --git a/ui/aura/client/default_activation_client.h b/ui/aura/client/default_activation_client.h
index ebf04aa86eb047b76f65f4903a468417b8012919..842ee909d624b4b4cdc1f94e776347174db682bf 100644
--- a/ui/aura/client/default_activation_client.h
+++ b/ui/aura/client/default_activation_client.h
@@ -5,14 +5,16 @@
 #ifndef UI_AURA_CLIENT_DEFAULT_ACTIVATION_CLIENT_H_
 #define UI_AURA_CLIENT_DEFAULT_ACTIVATION_CLIENT_H_
 
+#include <vector>
+
 #include "base/compiler_specific.h"
 #include "base/logging.h"
+#include "base/observer_list.h"
 #include "ui/aura/aura_export.h"
 #include "ui/aura/client/activation_client.h"
 #include "ui/aura/window_observer.h"
 
 namespace aura {
-class RootWindow;
 namespace client {
 class ActivationChangeObserver;
 }
@@ -25,7 +27,7 @@ namespace client {
 class AURA_EXPORT DefaultActivationClient : public client::ActivationClient,
                                             public WindowObserver {
  public:
-  explicit DefaultActivationClient(RootWindow* root_window);
+  explicit DefaultActivationClient(Window* root_window);
   virtual ~DefaultActivationClient();
 
   // Overridden from client::ActivationClient: